Question: "What does it mean to live by faith (Galatians 2:20)?"
Answer: The book of Galatians was a corrective letter written by Paul to the people within the region of Galatia. The Christians there were being convinced that the law of Moses must be followed even though such legalistic demands are contrary to the gospel of Jesus Christ (Galatians 2:21; 3:1–5). The people of Galatia were “deserting Him who called you by the grace of Christ, for a different gospel” (Galatians 1:6, NASB). Ultimately, this “different gospel” taught that, while Christ may have declared the Christian righteous at the point of belief, one was still required to live a life under the burden of the Mosaic Law. The people of Galatia were living according to the works of the law, not by faith, and Paul sets for them the example of how to “live by faith” (Galatians 2:20).
Whenever someone believes the gospel of Jesus Christ (1 Corinthians 15:3–5), that person is identified with Christ in the past (being positionally declared righteous), present (growing into righteousness), and future (being presented as perfectly righteous). Both the past and present aspects are seen in Galatians 2:20: “I have been crucified with Christ and I no longer live, but Christ lives in me. The life I now live in the body, I live by faith in the Son of God, who loved me and gave himself for me.” Paul contrasts living by faith with dying to the law: “through the law I died to the law so that I might live for God” (verse 19). This truth is further expounded in Galatians 3:3, “Are you so foolish? Having begun by the Spirit, are you now being perfected by the flesh?” (NASB). The implied answer is “no!” It is by faith, apart from the law, that one is presently being perfected.
Paul utilizes the concept of being “in Christ” (or “in the Lord”) 13 times in the book of Galatians. Instances of this point to the position of the Christian church (Galatians 1:22); the freedom the Christian has because of Christ (Galatians 2:4); the justification one receives through Christ (verse 17); the means by which one should live (verse 20); etc. (for all instances, see Galatians 1:16; 3:14, 19, 26, 28; 5:6, 10; 6:14).
The idea that we live by faith focuses on the present aspect of the Christian’s identity in Christ. In Galatians 2:20, Paul utilizes the phrase “in the body,” pointing specifically to the physical life of the Christian, as lived “now.” Living by faith is an act that takes place while the Christian is alive on the earth. This idea of presently being “in Christ” is critical to living by faith.
What is the object of the faith by which one should live? Paul continues in Galatians 2:20, “and the life which I now live in the flesh I live by faith in the Son of God, who loved me and gave Himself up for me” (NASB, emphasis added). The object of the belief, trust, or faith by which the Christian is to live is Jesus Christ! To live by faith is to live trusting Jesus, who loved us to the point of dying in our place (John 3:16), purchasing our salvation. This trust should be a constant throughout the life of the believer.
The Galatians were being told to live by works, ultimately placing the power in themselves. The gospel tells us that Jesus accomplished the necessary work; Jesus paid the price, and it is through Jesus that the Christian has freedom and power to live as he or she ought. The Christian is justified by faith in Jesus (Galatians 3:10–14; Romans 4:3; Titus 3:5), progressively made holy by faith in Jesus (Galatians 2:20; Titus 2:11–15), and glorified because of faith in Jesus (Romans 8:1, 28–30). All praise, honor, and glory are given to Jesus Christ, the Savior of the world (1 John 2:1–2).