Now I make known to you. This is the most powerful argument, the main hinge on which the question turns, that he has not received the gospel from men, but that it has been revealed to him by God. As this might be denied, he offers a proof, drawn from a narrative of facts. To give his declaration the greater weight, he sets out with stating that the matter is not doubtful, [1] but one which he is prepared to prove; and thus introduces himself in a manner well adapted to a serious subject. He affirms that it is not according to man; that it savours of nothing human, or, that it was not of human contrivance; and in proof of this he afterwards adds, that he had not been instructed by any earthly teacher. [2]

Footnotes

1 - "Qu'il ne parle point d'une chose incertaine ou incognue." "That he does not speak about a thing uncertain or unknown."

2 - "The idiom by which there is a transposition of hoti is frequent, and may here, Schott thinks, have been made use of, in order to place a highly important topic in the most prominent point of view" -- Bloomfield.

But I certify you - I make known to you; or, I declare to you; see 1-Corinthians 15:1. Doubtless this had been known to them before, but he now assures them of it, and goes into an extended illustration to show them that he had not received his authority from man to preach the gospel To state and prove this is the main design of this chapter.
Is not after man - The Greek text: "Not according to man"; see Galatians 1:1. That is, he was not appointed by man, nor did he have any human instructor to make known to him what the gospel was. He had neither received it from man, nor had it been debased or adulterated by any human admixtures. He had received it directly from the Lord Jesus.

But I certify you, brethren, etc. - I wish you fully to comprehend that the Gospel which I preached to you is not after man; there is not a spark of human invention in it, nor the slightest touch of human cunning.

(6) But I certify you, brethren, that the gospel which was preached of me is not after man.
(6) A second argument to prove that his doctrine is heavenly, because he had it from heaven, from Jesus Christ himself, without any man's help, in which he excels those whom Christ taught here on earth after the manner of men.

But I certify you, brethren,.... Though the Galatians had gone such lengths with their false teachers, yet the apostle still calls them "brethren"; as hoping well of them, that they were born of God, did belong to his family, and were heirs of the grace of life; and this he the rather makes use of, to show his affection to them, and to engage their attention to the assurance he gives, of the divine original and authority of the Gospel preached by him; which though they formerly knew and believed, yet through the insinuations of the false apostles, were drawn into some doubts about it: wherefore he declares in the most solemn and affectionate manner,
that the Gospel which was preached of me, is not after man. Their guides that were leading them wrong, did not presume to say, that the Gospel was after man, for they themselves pretended to preach the Gospel; but that the Gospel preached by the apostle had no other authority than human, or than his own to support it: wherefore he denies that it was "after man"; after the wisdom of man, an human invention and contrivance, a device and fiction of man's brain; nor was it after the mind of man, or agreeably to his carnal reason, it was disapproved of by him, and beyond his capacity to reach it; nor was it of his revealing, a discovery of his; flesh and blood, human nature, could never have revealed it; nor is it in the power of one man to make another a minister of the Gospel, or to give him or himself success in the ministration of it, but the whole is of God.

certify--I made known to you as to the Gospel which was preached by me, that it is not after man, that is, not of, by, or from man (Galatians 1:1, Galatians 1:12). It is not according to man; not influenced by mere human considerations, as it would be, if it were of human origin.
brethren--He not till now calls them so.

The gospel which was preached by me is not after to man. It is not preached to please man, nor is it of human origin.
For I neither received it of man, etc. It could not be of man, for it did not come to him from man. No preacher or apostle taught it to him, but it came by a direct revelation of Christ. The first revelation was on the way to Damascus (Acts 26:13-18). There were no doubt successive revelations (2-Corinthians 12:1).

But I certify you, brethren - He does not till now give them even this appellation. That the gospel which was preached by me among you is not according to man - Not from man, not by man, not suited to the taste of man.