2 Timothy 1:1

Paul an apostle of Jesus Christ
Not of men, nor by men, but by Jesus Christ, from whom he was sent; by whom he was qualified; in whose name he came, and ministered; and whom he preached. Of his name Paul, and of his office, as an apostle, (See Gill on Romans 1:1) into which office he came

by the will of God;
not by the will of man, no, not of the best of men, of James, Cephas, or John, or any of the other apostles; nor by his own will, he did not thrust himself into this office, or take this honour upon himself; nor was it owing to any merits of his, which he always disclaims, but to the will and grace of God; it was by the secret determining will of God, that he was from all eternity separated unto the Gospel of Christ; and it was by the revealed will of God to the church, that he, with Barnabas, was set apart to the ministry of the word; see ( Romans 1:1 ) ( Acts 13:2 ) .

According to the promise of life which is in Christ Jesus;
or "with respect unto it"; this points at the sum and substance, or subject matter, and end of his apostleship, for which this grace was given to him, which was to publish the free promise of life and salvation by Jesus Christ. By "life" here is meant, not this corporeal life, which, and a continuation of it, were promised in the covenant of works, on condition of man's obedience to it; but eternal life, the promise of which is a free promise made by God, of his own free sovereign will and pleasure, in the covenant of grace, from everlasting; and is an absolute and unconditional one, not at all depending upon the works of the law, or obedience to it; see ( Romans 14:16 ) ( Galatians 3:18 ) and this promise is "in Christ", in whom all the promises are yea and arisen: for it was made before the world began, ( Titus 1:2 ) when the persons on whose account it was made were not in actual being; but Christ, their head and representative, then existed; and to him it was given, and into his hands was it put for them, where it is sure to all the seed; and not only the promise, but the life itself is in him, and which is here intended. Christ, as Mediator, asked it of his Father for all his people, and he gave it to him, where it is hid safe and secure. Christ is the Prince or author of life; he is the procuring cause of it; he was sent, and came, that his sheep might have it; he gave his flesh, his human nature for it; and by his sufferings and death removed all obstructions which sin had thrown in the way, and opened the way for their enjoyment of it; and he is the giver of it to as many as the Father has given him; nor is it to be had in any other way, or of any other; but of him; and it lies in the knowledge of him, communion with him, and conformity to him. Now it is the business, of Gospel ministers, not to direct persons to work for life, or to seek to obtain eternal life by their own works of righteousness, but to hold forth the word of life, or to show men the way of life and salvation by Christ alone.