Let brotherly love, etc. Probably he gave this command respecting brotherly love, because a secret hatred arising from the haughtiness of the Jews was threatening to rend the Churches. But still this precept is generally very needful, for nothing flows away so easily as love; when everyone thinks of himself more than he ought, he will allow to others less than he ought; and then many offenses happen daily which cause separations. [1] He calls love brotherly, not only to teach us that we ought to be mutually united together by a peculiar and an inward feeling of love, but also that we may remember that we cannot be Christians without being brethren; for he speaks of the love which the household of faith ought to cultivate one towards another inasmuch as the Lord has bound them closer together by the common bond of adoption. It was therefore a good custom in the primitive Church for Christians to call one another brothers; but now the name as well as the thing itself is become almost obsolete, except that the monks have appropriated to themselves the use of it when neglected by others, while at the same time they show by their discords and intestine factions that they are the children of the evil one.

Footnotes

1 - "Continue" or remain, implies that they had manifested this love, chapter 6:10; as though he had said, "Let the love of the brethren be such as it has been." -- Ed.

Let brotherly love continue - Implying that it now existed among them. The apostle had no occasion to reprove them for the want of it, as he had in regard to some to whom he wrote, but he aims merely to impress on them the importance of this virtue, and to caution them against the danger of allowing it ever to be interrupted; see the notes on John 13:34.

Let brotherly love continue - Be all of one heart and one soul.
Feel for, comfort, and support each other; and remember that he who professes to love God should love his brother also. They had this brotherly love among them; they should take care to retain it. As God is remarkable for his φιλανθρωπια, philanthropy, or love to man, so should they be for φιλαδελφια, or love to each other. See the note on Titus 3:4.

Let (1) brotherly love continue.
(1) He comes to the second table of the law, the sum of which is charity, especially toward strangers and such as are afflicted.

Let brotherly love continue. The Vulgate Latin and Syriac versions add, "in you"; or among you, as a church and society of Christians; for this is not to be understood of love to all mankind, or to those of the same nation, or who are in a strict natural relation brethren, though they are all in a sense brethren, and to be loved; but of love to those who are in the same spiritual relation to God, as their Father, to Christ, as the firstborn among many brethren; and are in the same church state, at least partakers of the same grace: and which love ought to be universal, and reach to all the saints, and be fervent and unfeigned, and as Christ hath loved us; and when it is genuine, it is active and laborious; and shows itself in praying with and for one another; in bearing one another's burdens; in forbearing and forgiving one another; in admonishing one another in love; in building up each other in the most holy faith; and in stirring up one another to the several duties of religion: and without this excellent and useful grace, a profession of religion is in vain; this is an evidence of regeneration; it is the bond of perfectness, and what renders the saints' communion delightful and edifying: many are the arguments moving to the exercise of it; as the love of God, and Christ; the new commandment of Christ; the relation saints stand in to one another; the comfort and joy of Gospel ministers, and our own peace and edification: and this should continue; for the love of God and Christ continues; the relation between the saints continues; and without this, churches cannot continue long: the apostle means, not the grace itself, the internal principle, for that, where it once is, always continues, and can never be lost; but the exercise and increase of it, an abounding in it yet more and more. One of the Jewish prayers is to this purpose (q);
"he that dwells in this house, let him plant among you , "brotherhood and love", (or brotherly love,) peace and friendship.''
(q) T. Hieros. Beracot, fol. 3. 3.

The design of Christ in giving himself for us, is, that he may purchase to himself a peculiar people, zealous of good works; and true religion is the strongest bond of friendship. Here are earnest exhortations to several Christian duties, especially contentment. The sin opposed to this grace and duty is covetousness, an over-eager desire for the wealth of this world, with envy of those who have more than ourselves. Having treasures in heaven, we may be content with mean things here. Those who cannot be so, would not be content though God raised their condition. Adam was in paradise, yet not contented; some angels in heaven were not contented; but the apostle Paul, though abased and empty, had learned in every state, in any state, to be content. Christians have reason to be contented with their present lot. This promise contains the sum and substance of all the promises; "I will never, no, never leave thee, no, never forsake thee." In the original there are no less than five negatives put together, to confirm the promise: the true believer shall have the gracious presence of God with him, in life, at death, and for ever. Men can do nothing against God, and God can make all that men do against his people, to turn to their good.

EXHORTATION TO VARIOUS GRACES, ESPECIALLY CONSTANCY IN FAITH, FOLLOWING JESUS AMIDST REPROACHES. CONCLUSION, WITH PIECES OF INTELLIGENCE AND SALUTATIONS. (Hebrews. 13:1-25)
brotherly love--a distinct special manifestation of "charity" or "love" (2-Peter 1:7). The Church of Jerusalem, to which in part this Epistle was addressed, was distinguished by this grace, we know from Acts (compare Hebrews 6:10; Hebrews 10:32-34; Hebrews 12:12-13).
continue--Charity will itself continue. See that it continue with you.

Let brotherly love continue. The love which binds brethren in the church together.
Be not forgetful to entertain strangers. Hospitality is a duty often emphasized in the New Testament. Here it assumes the form of receiving stranger saints. Often they were driven from their homes by persecution, and the church elsewhere was wont to open its homes to them.
Some have entertained angels unawares. See Genesis 18:1-3. Also Matthew 25:35.
Remember them that are in bonds. Another manifestation of brotherly love. The prisoners referred to are those imprisoned for Christ's sake. The Christian must enter into full sympathy with all his suffering brethren.

Brotherly love is explained in the following verses.