John Wesley's Notes:
    The Apostle goes on to describe how he is freed from sin; how far he is from continuing therein.

I am crucified with Christ-Made conformable to his death; the body of sin is destroyed. Ro 6:6.

And I-As to my corrupt nature.

Live no longer-Being dead to sin.

But Christ liveth in me-Is a fountain of life in my inmost soul, from which all my tempers, words, and actions flow.

And the life that I now live in the flesh-Even in this mortal body,

I live by faith in the Son of God-I derive every moment from that supernatural principle; from a divine evidence and conviction, that he loved me, and delivered up himself for me.
 

Albert Barnes' Commentary:
  I am crucified with Christ. In the previous verse, Paul had said that he was dead. In this verse he states what he meant by it, and shows that he did not wish to be understood as saying that he was inactive, or that he was literally insensible to the appeals made to him by other beings and objects. In respect to one thing he was dead; to all that was truly great and noble he was alive. To understand the remarkable phrase, "I am crucified with Christ," we may remark,

(1.) that this was the way in which Christ was put to death. He suffered on a cross, and thus became literally dead.

(2.) In a sense similar to this, Paul became dead to the law, to the world, and to sin. The Redeemer, by the death of the cross, became insensible to all surrounding objects, as the dead always are. He ceased to see and hear, and was as though they were not. Hie was laid in the cold grave, and they did not affect or influence him. So Paul says that he became insensible to the law as a means of justification; to the world; to ambition and the love of money; to the pride and pomp of life; and to the dominion of evil and hateful passions. They lost their power over him; they ceased to influence him.

(3.) This was with Christ, or by Christ. It cannot mean literally that he was put to death with him, for that is not true; but it means that the effect of the death of Christ on the cross was to make him dead to these things, in like manner as he, when he died, became insensible to the things of this busy world. This may include the following things:

(a) There was an intimate union between Christ and his people; so that what affected him, affected them. See Joh 15:5,6.

(b) The death of the Redeemer on the cross involved as a consequence the death of his people to the world and to sin. See Ga 5:24; 6:14. It was like a blow at the root of a vine or a tree, which would affect every branch and tendril; or like a blow at the head, which affects every member of the body.

(c) Paul felt identified with the Lord Jesus; and he was willing to share in all the ignominy and contempt which was connected with the idea of the crucifixion. He was willing to regard himself as one with the Redeemer. If there was disgrace attached to the manner in which he died, he was willing to share it with him. He regarded it as a matter to be greatly desired to be made just like Christ in all things, and even in the manner of his death. This idea he has more fully expressed in Php 3:10, "That I may know him, [that is, I desire earnestly to know him,] and the power of his resurrection, and the fellowship of his sufferings, being made conformable unto his death." See also Col 1:24; 1Pe 4:13.

Nevertheless I live. This expression is added, as in Ga 2:19, to prevent the possibility of mistake. Paul, though he was crucified with Christ, did not wish to be understood that he felt himself to be dead. He was not inactive; not insensible, as the dead are, to the appeals which are made from God, or to the great objects which ought to interest an immortal mind. He was still actively employed, and the more so from the fact that he was crucified with Christ. The object of all such expressions as this is to show that it was no design of the gospel to make men inactive, or to annihilate their energies. It was not to cause men to do nothing. It was not to paralyze their powers, or stifle their own efforts. Paul therefore says, "I am not dead. I am truly alive; and I live a better life than I did before." Paul was as active after conversion as he was before. Before, he was engaged in persecution; now, he devoted his great talents with as much energy, and with as untiring zeal, to the cause of the great Redeemer. Indeed, the whole narrative would lead us to suppose that he was more active and zealous after his conversion than he was before. The effect of religion is not to make one dead in regard to the putting forth of the energies of the soul. True religion never made one lazy man; it has converted many a man of indolence, and effeminacy, and self-indulgence, to a man actively engaged in doing good. If a professor of religion is less active in the service of God than he was in the service of the world--less laborious, and zealous, and ardent than he was before his supposed conversion--he ought to set it down as full proof that he is an utter stranger to true religion.

Yet not I. This also is designed to prevent misapprehension. In the previous clause he had said that he lived, or was actively engaged. But lest this should be misunderstood, and it should be inferred that he meant to say it was by his own energy or powers, he guards it, and says it was not at all from himself. It was by no native tendency; no power of his own; nothing that could be traced to himself, he assumed no credit for any zeal which he had shown in the true life. He was disposed to trace it all to another. He had ample proof in his past experience that there was no tendency in himself to a life of true religion, and he therefore traced it all to another.

Christ liveth in me. Christ was the source of all the life that he had. Of course this cannot be taken literally that Christ had a residence in the apostle; but it must mean that his grace resided in him; that his principles actuated him; and that he derived all his energy, and zeal, and life from his grace. The union between the Lord Jesus and the disciple was so close that it might be said the one lived in the other. So the juices of the vine are in each branch, and leaf, and tendril, and live in them and animate them; the vital energy of the brain is in each delicate nerve--no matter how small--that is found in any part of the human frame. Christ was in him, as it were, the vital principle. All his life and energy were derived from him.

And the life which I now live in the flesh. As I now live on the earth, surrounded by the cares and anxieties of this life. I carry the life-giving principles of my religion to all my duties and all my trials.

I live by the faith of the Son of God. By confidence in the Son of God, looking to him for strength, and trusting in his promises and in his grace.

Who loved me, etc. He felt under the highest obligation to him, from the fact that he had loved him, and given himself to the death of the cross in his behalf. The conviction of obligation on this account Paul often expresses. See Barnes for Ro 6:8 and Ro 6:9-11 See Barnes for Ro 8:35, and Ro 8:36-39; See Barnes for 2Co 5:15. There is no higher sense of obligation than that which is felt towards the Saviour; and Paul felt himself bound, as we should, to live entirely to him who had redeemed him by his blood.

{a} "crucified with Christ" Ga 5:24; 6:14
{b} "liveth in me" 1Th 5:10; 1Pe 4:2
{c} "gave himself" Joh 10:11; Eph 5:2