The “I live; yet not I, but Christ liveth in me” in Galatians 2:20 does not mean that Paul actually did not live the Christian life and the Lord Jesus lived it instead of him. Such a conclusion would neglect the fact that Paul specifically says “I live.” Furthermore, Paul does not say, “Christ liveth instead of me,” but “Christ liveth in me.” The preposition en, not anti or huper, is employed. The “yet not I” clause means simply that Paul did not have strength sourced in himself to follow the Lord, but he received grace from Christ to enable him to “work out [his] own salvation with fear and trembling [since] it is God which worke[d] in [him] both to will and to do of his good pleasure” (Philippians 2:12-13). Paul personally “strived” to serve the Lord, but nonetheless his service was what “Christ hath . . . wrought by [him]” (Romans 15:20, 18). Parallel Pauline texts shed much light on the “not I, but Christ” portion of Galatians 2:20:
1.) “And unto the married I command, yet not I, but the Lord, Let not the wife depart from her husband.” (1 Corinthians 7:10). Paul certainly did command the wife not to depart from her husband. He was very active in making this command. However, more importantly, it was God Himself who made the command through Paul. It would be poor exegesis to conclude from this verse that Paul himself did not really command wives not to leave their husbands because the command was sourced in God.
2.) But by the grace of God I am what I am: and his grace which was bestowed upon me was not in vain; but I laboured more abundantly than they all: yet not I, but the grace of God which was with me” (1 Corinthians 15:10). Obviously God’s enabling grace strengthened Paul to work, and all the glory for Paul’s labor was given to the grace of God, as is evidenced by the “yet not I, but the grace of God” affirmation. Nonetheless, Paul labored very actively and fervently, indeed, “more abundantly than . . . all.” It would be poor exegesis to conclude from this verse that Paul really did not labor at all because his ability to labor came from God.
3.) “Now then it is no more I that do it [transgress], but sin that dwelleth in me . . . . Now if I do that I would not, it is no more I that do it, but sin that dwelleth in me.” (Romans 7:17, 20; cf. Romans 7:14-25). Before Paul was converted, his entire being consented to and produced nothing but sin. His statement in Romans 7:17, 20 means that the sins that he did as a regenerate person no longer proceeded from the unified desire of his whole person. Rather, Paul’s transgressions were now sourced in the remnants of sinfulness that remained within him. Nonetheless, whenever Paul sinned, the Apostle was by no means passively employed by some exterior agent moving him unconsciously to transgress—he still chose to do so himself.
4.) The Old Testament, and other New Testament texts, present a similar picture. Joseph tells his brothers in Genesis 45:8: “So now it was not you that sent me hither, but God; and he hath made me a father to Pharaoh, and lord of all his house, and a ruler throughout all the land of Egypt.” Joseph’s “not you . . . but God” statement does not mean that Joseph’s brothers did not sell him into slavery (cf. 45:5, “ye sold me hither”), but simply that God was the ultimate sovereign source of his being sold. In Exodus 16:8, “Moses said . . . [T]he LORD heareth your murmurings which ye murmur against him: and what are we? your murmurings are not against us, but against the LORD,” but the affirmation that Israel’s grumbling was ultimately against Jehovah certainly did not mean that when “the whole congregation of the children of Israel murmured against Moses and Aaron in the wilderness” (Exodus 16:2) they did not really murmur against Moses and Aaron.
Similarly, Paul’s “not I, but Christ” statement in Galatians 2:20 means that the source of the Christian life that Paul lived was not his own inherent ability or strength, but Christ’s grace and power. The Apostle’s declaration models the pattern set by his Savior, that Son of Man who stated “I can of mine own self do nothing” (John 5:30) and “The Son can do nothing of himself, but what he seeth the Father do: for what things soever he doeth, these also doeth the Son likewise” (John 5:19). The Lord Jesus, in His human nature, was entirely submissive to and dependent upon the enablement He received beyond measure from God. One sees, however, extremely active labor for the Lord in the incarnate Christ. The Divine Person of the Son also did not work independently of the Person of the Father, but nonetheless the Son of God actively did whatsoever He saw the Father do.
In Galatians 2:19-21 Paul is proving that he is dead to the law (2:19a) and not trusting in the law for salvation and frustrating the grace of God by so doing (2:21) but instead is living unto God (2:19b, 2:20). He is not proving that somehow he does not live the Christian life but Christ lives it instead. Paul and all Christians are given strength and grace from Christ, apart from whom they can do nothing good, John 15:5, and they are to live by faith. Certainly the facts of the saint’s union with Christ, the Savior’s indwelling presence, the spiritual life that is derived from Him, and the power He gives believers to will and do of His good pleasure are glorious truths worthy of that joyful acceptance and humble meditation that results in loving, faith-based obedience. However, to go beyond the actual declarations of Galatians 2:20 to say that the believer does not live the Christian life but Christ Himself does it instead is to make the verse affirm what it does not say and thus grieve the Spirit and displease Christ. Such an affirmation also confuses the Christian who believes it, hinders his sanctification, and opens the way to serious Christological error. The glorious truths of Galatians 2:20 should neither be minimized and ignored nor turned into something other than they are by illegitimate extrapolation.
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 For example, Christ tells persecuted believers: “But when they shall lead you, and deliver you up, take no thought beforehand what ye shall speak, neither do ye premeditate: but whatsoever shall be given you in that hour, that speak ye: for it is not ye that speak, but the Holy Ghost” (Mark 13:11; cf. Matthew 10:19-20; Luke 12:11-12; 21:14-15). The Lord Jesus’ statement, “it is not ye that speak, but the Holy Ghost,” did not mean that the persecuted saints in question did not actually open their mouths and consciously speak; rather, they indeed spoke, but the Spirit directed them and guided them. Thus, the Lord could command, “speak ye,” for the very reason (“for”) that their words did not originate in themselves (“it is not ye that speak”) but in God the Spirit. Note the following related texts: Matthew 10:40; Mark 9:37; Luke 10:16; John 12:44; 13:20; Romans 13:2; 1 Thessalonians 4:8.