*Minor differences ignored. Grouped by changes, with first version listed as example.
If the Lord will. A twofold condition is laid down, "If we shall live so long," and, "If the Lord will;" because many things may intervene to upset what we may have determined; for we are blind as to all future events.  By will he means not that which is expressed in the law, but God's counsel by which he governs all things.
1 - The words may be rendered thus, "If the Lord will, we shall both live and do this or that." So that living and doing are both dependent on God's will.
For that ye ought to say - Instead of what you do say, "we will go into such a city," you ought rather to recognise your absolute dependence on God, and feel that life and success are subject to his will. The meaning is not that we ought always to be saying that in so many words, for this might become a mere ostentatious form, offensive by constant unmeaning repetition; but we are, in the proper way, to recognise our dependence on him, and to form all our plans with reference to his will.
If the Lord will - This is proper, because we are wholly dependent on him for life, and as dependent on him for success. He alone can keep us, and he only can make our plans prosperous. In a thousand ways he can thwart our best-laid schemes, for all things are under his control. We need not travel far in life to see how completely all that we have is in the hands of God, or to learn how easily he can frustrate us if he pleases. There is nothing on which the success of our plans depends over which we have absolute control; there is nothing, therefore, on which we can base the assurance of success but his favor.
For that ye ought to say - Αντι τοι λεγειν ὑμας· Instead of saying, or instead of which ye should say,
If the Lord will, we shall live - I think St. James had another example from the rabbins in view, which is produced by Drusius, Gregory, Cartwright, and Schoettgen, on this clause: "The bride went up to her chamber, not knowing what was to befall her there." On which there is this comment: "No man should ever say that he will do this or that, without the condition If God Will. A certain man said, 'To-morrow shall I sit with my bride in my chamber, and there shall rejoice with her.' To which some standing by said, אם גוזר השם im gozer hashshem, 'If the Lord will.' To which he answered, 'Whether the Lord will or not, to-morrow will I sit with my bride in my chamber.' He did so; he went with his bride into his chamber, and at night they lay down; but they both died, antequam illam cognosceret." It is not improbable that St. James refers to this case, as he uses the same phraseology.
On this subject I shall quote another passage which I read when a schoolboy, and which even then taught me a lesson of caution and of respect for the providence of God. It may be found in Lucian, in the piece entitled, Χαρων, η επισκοπουντες, c. 6: Επι δειπνον, οιμαι, κληθεις ὑπο τινος των φιλων ες την ὑστεραιαν, μαλιστα ἡξω, εφη· και μεταξυ λεγοντος, απο του τεγους κεραμις επιπεσουσα, ουκ οιδ' ὁτου κινησαντος, απεκτεινεν αυτον· εγελασα ουν, ουκ επιτελεσαντος την ὑποσχεσιν. "A man was invited by one of his friends to come the next day to supper. I will certainly come, said he. In the mean time a tile fell from a house, I knew not who threw it, and killed him. I therefore laughed at him for not fulfilling his engagement." It is often said Fas est et ab hoste doceri, " we should learn even from our enemies." Take heed, Christian, that this heathen buffoon laugh thee not out of countenance.
For that ye ought to say,.... Instead of saying we will go to such and such a place, and do this, and that, and the other thing, it should be said,
if the Lord will, and we shall live, and do this and that; the last "and" is left out in the Vulgate Latin, Syriac, Arabic, and Ethiopic versions; and the passage rendered thus, "if the Lord will, and we shall live, we will do this": so that here are two conditions of doing anything; the one is, if it should be agreeable to the determining will and purpose of God, by which everything in the world comes to pass, and into which the wills of men should be resolved, and resigned; and the other is, if we should live, since life is so very uncertain and precarious: and the sense is, not that this exact form of words should be always used, but what is equivalent to them, or, at least, that there should be always a sense of these things upon the mind; and there should be a view to them in all resolutions, designs, and engagements: and since the words are so short and comprehensive, it might be proper for Christians to use themselves to such a way of speaking; upon all occasions; we find it used by the Apostle Paul frequently, as in Acts 18:2, and even by Jews, Heathens, and Turks. It is a saying of Ben Syra, the Jew (p),
"let a man never say he will do anything, before he says , "if God will"''
So Cyrus, king of Persia, when, under pretence of hunting, he designed an expedition into Armenia, upon which an hare started, and was caught by an eagle, said to his friends, this will be a good or prosperous hunting to us, , "if God will" (q). And very remarkable are the words of Socrates to Alcibiades, inquiring of him how he ought to speak; says Socrates, , "if God will" (r); and says he, in another place (s),
"but I will do this, and come unto thee tomorrow, "if God will".''
And it is reported of the Turks (t), that they submit everything to the divine will; as the success of war, or a journey, or anything, even of the least moment, they desire to be done; and never promise themselves, or others, anything, but under this condition, "In Shallah", if God will.
(p) Sentent. 11. (q) Xenophon. Cyropaed. l. 2. c. 25. (r) Plato in Aleibiade, p. 135. (s) Plato in Laches. (t) Smith de Moribus Turc. p. 74.
Literally, "instead of your saying," &c. This refers to "ye that say" (James 4:13).
we shall live--The best manuscripts read, "We shall both live and do," &c. The boasters spoke as if life, action, and the particular kind of action were in their power, whereas all three depend entirely on the will of the Lord.
Instead of your saying - That is, whereas ye ought to say.
*More commentary available at chapter level.