*Minor differences ignored. Grouped by changes, with first version listed as example.
For we have not, etc. There is in the name which he mentions, the Son of God, such majesty as ought to constrain us to fear and obey him. But were we to contemplate nothing but this in Christ, our consciences would not be pacified; for who of us does not dread the sight of the Son of God, especially when we consider what our condition is, and when our sins come to mind? The Jews might have had also another hindrance, for they had been accustomed to the Levitical priesthood; they saw in that one mortal man, chosen from the rest, who entered into the sanctuary, that by his prayer he might reconcile his brethren to God. It is a great thing, when the Mediator, who can pacify God towards us, is one of ourselves. By this sort of allurement the Jews might have been ensnared, so as to become ever attached to the Levitical priesthood, had not the Apostle anticipated this, and showed that the Son of God not only excelled in glory, but that he was also endued with equal kindness and compassion towards us. It is, then, on this subject that he speaks, when he says that he was tried by our infirmities, that he might condole with us. As to the word sympathy, (sumpatheia,) I am not disposed to indulge in refinements; for frivolous, no less than curious, is this question, "Is Christ now subject to our sorrows?" It was not, indeed, the Apostle's object to weary us with such subtleties and vain speculations, but only to teach us that we have not to go far to seek a Mediator, since Christ of his own accord extends his hand to us, that we have no reason to dread the majesty of Christ since he is our brother, and that there is no cause to fear, lest he, as one unacquainted with evils, should not be touched by any feelings of humanity, so as to bring us help, since he took upon him our infirmities, in order that he might be more inclined to succor us.  Then the whole discourse of the Apostle refers to what is apprehended by faith, for he does not speak of what Christ is in himself, but shows what he is to us. By the likeness, he understands that of nature, by which he intimates that Christ has put on our flesh, and also its feelings or affections, so that he not only paroled himself to be real man, but had also been taught by his own experience to help the miserable; not because the Son of God had need of such a training, but because we could not otherwise comprehend the care he feels for our salvation. Whenever, then, we labor under the infirmities of our flesh, let us remember that the Son of God experienced the same, in order that he might by his power raise us up, so that we may not be overwhelmed by them. But it may be asked, What does he mean by infirmities? The word is indeed taken in various senses. Some understand by it cold and heat; hunger and other wants of the body; and also contempt, poverty, and other things of this mind, as in many places in the writings of Paul, especially in 2-Corinthians 12:10. But their opinion is more correct who include, together with external evils, the feelings of the souls such as fear, sorrow, the dread of death, and similar things.  And doubtless the restriction, without sin, would not have been added, except he had been speaking of the inward feelings, which in us are always sinful on account of the depravity of our nature; but in Christ, who possessed the highest rectitude and perfect purity, they were free from everything vicious. Poverty, indeed, and diseases, and those things which are without us, are not to be counted as sinful. Since, therefore, he speaks of infirmities akin to sin, there is no doubt but that he refers to the feelings or affections of the mind, to which our nature is liable, and that on account of its infirmity. For the condition of the angels is in this respect better than ours; for they sorrow not, nor fear, nor are they harassed by variety of cares, nor by the dread of death. These infirmities Christ of his own accord undertook, and he willingly contended with them, not only that he might attain a victory over them for us, but also that we may feel assured that he is present with us whenever we are tried by them. Thus he not only really became a man, but he also assumed all the qualities of human nature. There is, however, a limitation added, without sin; for we must ever remember this difference between Christ's feelings or affections and ours, that his feelings were always regulated according to the strict rule of justice, while ours flow from a turbid fountain, and always partake of the nature of their source, for they are turbulent and unbridled. 
1 - Calvin has followed the Vulg. In rendering this clause, "who cannot sympathize (compati) with our infirmities." Our version is that of Eramus and Beza. The meaning may thus be given, "Who cannot feel for us in our infirmities." -- Ed.
2 - The word "infirmities" is often used metonymically for things which we are too weak to bear, even trials and temptations. Christ, our high priest, feels for us in all those straits and difficulties, whatever they be, which meet us in our course, and make us feel and know our weaknesses. -- Ed.
3 - The common idea of what is here said is, that Christ though tried and tempted, was not yet guilty of sin, or did not fall into sin. That he had no sin, that he was without sin, is what we plainly learn from 2-Corinthians 5:21; 1 John 3:5, etc.; but is this what is taught here? The clause, I conceive, may be thus rendered, -- "But was in all things tried in like manner except sin;" that is, with the exception that he had no innate sin to contend with. The last words are literally, "in likeness with the exclusion of sin," which seems to import that it was a likeness with the exclusion of sin. But if the words "except (or without) sin" do not qualify "likeness," they must be connected with "tried" or tempted, and thus rendered, -- "But was in like manner tried in all things without sin;" that is, without sinning, or falling into sin. The difference is, that in the one sense Christ had no inward sin to contend with, and that in the other he withstood temptation without falling into sin. Both senses are true, and either of them will suit this passage. -- Ed.
For we have not an high priest which cannot be touched - Our High Priest is not cold and unfeeling. That is, we have one who is abundantly qualified to sympathize with us in our afflictions, and to whom, therefore, we may look for aid and support in trials. Had we a high priest who was cold and heartless; who simply performed the external duties of his office without entering into the sympathies of those who came to seek for pardon; who had never experienced any trials, and who felt himself above those who sought his aid, we should necessarily feel disheartened in attempting to overcome our sins, and to live to God. His coldness would repel us; his stateliness would awe us; his distance and reserve would keep us away, and perhaps render us indifferent to all desire to be saved. But tenderness and sympathy attract those who are feeble, and kindness does more than anything else to encourage those who have to encounter difficulties and dangers; see the notes at Hebrews 2:16-18. Such tenderness and sympathy has our Great High Priest.
But was in all points tempted like as we are - "Tried" as we are; see the notes at Hebrews 2:18. He was subjected to all the kinds of trial to which we can be, and he is, therefore, able to sympathize with us and to aid us. He was tempted - in the literal sense; he was persecuted; he was poor; he was despised; he suffered physical pain; he endured the sorrows of a lingering and most cruel death.
Yet without sin - 1-Peter 2:22. "Who did no sin;" Isaiah 53:9, "He had done no violence, neither was there any deceit in his mouth;" Hebrews 7:26, "Who is holy, harmless, undefiled, separate from sinners." The importance of this fact - that the Great High Priest of the Christian profession was "without sin," the apostle illustrates at length in Hebrews. 7-9. He here merely alludes to it, and says that one who was "without sin" was able to assist those who were sinners, and who put their trust in him.
For we have not a high priest - To the objection, "Your High Priest, if entered into the heavens, can have no participation with you, and no sympathy for you, because out of the reach of human feelings and infirmities," he answers: Ου γαρ εχομεν Αρχιερεα μη δυναμενον συμπαθησαι ταις ασθενειαις ἡμων· We have not a high priest who cannot sympathize with our weakness. Though he be the Son of God, as to his human nature, and equal in his Divine nature with God; yet, having partaken of human nature, and having submitted to all its trials and distresses, and being in all points tempted like as we are, without feeling or consenting to sin; he is able to succor them that are tempted. See Hebrews 2:18, and the note there.
The words κατα παντα καθ' ὁμοιοτητα might be translated, in all points according to the likeness, i.e. as far as his human nature could bear affinity to ours; for, though he had a perfect human body and human soul, yet that body was perfectly tempered; it was free from all morbid action, and consequently from all irregular movements. His mind, or human soul, being free from all sin, being every way perfect, could feel no irregular temper, nothing that was inconsistent with infinite purity. In all these respects he was different from us; and cannot, as man, sympathize with us in any feelings of this kind: but, as God, he has provided support for the body under all its trials and infirmities, and for the soul he has provided an atonement and purifying sacrifice; so that he cleanses the heart from all unrighteousness, and fills the soul with his Holy Spirit, and makes it his own temple and continual habitation. He took our flesh and blood, a human body and a human soul, and lived a human life. Here was the likeness of sinful flesh, Romans 8:5; and by thus assuming human nature, he was completely qualified to make an atonement for the sins of the world.
(6) For we have not an high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as [we are, yet] without sin.
(6) Lest he appear by the great glory of our High Priest, to prevent us from going to him, he adds after, that he is nonetheless our brother indeed, (as he proved before) and that he counts all our miseries as his own, to call us boldly to him.
For we have not an high priest,.... That is cruel and unmerciful; the saints have an high priest, but not such an one:
which cannot be touched with the feeling of our infirmities; such as bodily diseases and wants, persecutions from men, and the temptations of Satan; under all which Christ sympathizes with his people; and which sympathy of his arises from his knowledge and experience of these things, and the share he has had of them, and from that union there is between him and his people: and it is not a bare sympathy, but is attended with his assistance, support, and deliverance; and the consideration of it is of great comfort to the saints:
but was in all points tempted like as we are: of the temptations of Christ, and of the saints; see Gill on Hebrews 2:18.
yet without sin; there was no sin in his nature; though he was encompassed about with infirmities, yet not with sinful infirmities, only sinless ones; nor was there any sin in his temptations; though he was solicited to sin by Satan, yet he could find none in him to work upon; nor could he draw him into the commission of any sin.
For--the motive to "holding our profession" (Hebrews 4:14), namely the sympathy and help we may expect from our High Priest. Though "great" (Hebrews 4:14), He is not above caring for us; nay, as being in all points one with us as to manhood, sin only excepted, He sympathizes with us in every temptation. Though exalted to the highest heavens, He has changed His place, not His nature and office in relation to us, His condition, but not His affection. Compare Matthew 26:38, "watch with me": showing His desire in the days of His flesh for the sympathy of those whom He loved: so He now gives His suffering people His sympathy. Compare Aaron, the type, bearing the names of the twelve tribes in the breastplate of judgment on his heart, when he entered into the holy place, for a memorial before the Lord continually (Exodus 28:29).
cannot be touched with the feeling of--Greek, "cannot sympathize with our infirmities": our weaknesses, physical and moral (not sin, but liability to its assaults). He, though sinless, can sympathize with us sinners; His understanding more acutely perceived the forms of temptation than we who are weak can; His will repelled them as instantaneously as the fire does the drop of water cast into it. He, therefore, experimentally knew what power was needed to overcome temptations. He is capable of sympathizing, for He was at the same time tempted without sin, and yet truly tempted [BENGEL]. In Him alone we have an example suited to men of every character and under all circumstances. In sympathy He adapts himself to each, as if He had not merely taken on Him man's nature in general, but also the peculiar nature of that single individual.
but--"nay, rather, He was (one) tempted" [ALFORD].
like as we are--Greek, "according to (our) similitude."
without sin--Greek, "choris," "separate from sin" (Hebrews 7:26). If the Greek "aneu" had been used, sin would have been regarded as the object absent from Christ the subject; but choris here implies that Christ, the subject, is regarded as separated from sin the object [TITTMANN]. Thus, throughout His temptations in their origin, process, and result, sin had nothing in Him; He was apart and separate from it [ALFORD].
He sympathizes with us even in our innocent infirmities, wants, weaknesses, miseries, dangers. Yet without sin - And, therefore, is indisputably able to preserve us from it in all our temptations.
*More commentary available at chapter level.