“And if you are Christ’s, then you are Abraham’s seed, and heirs according to the promise.”
The third privilege Christians have is that they are special “heirs” of God.
And if you are Christ’s, then you are Abraham’s seed,
Christians belong to Abraham’s seed. The running battle in Galatians concerned whether Gentiles must become Jews to be saved. Paul says that Christians are Abraham’s seed at the point they place their faith in Christ. This flew in the face of the Judaizers, who demanded a Christian must subsequently become a Jew as well as a Christian to be accepted by God.
The Christian receives eternal life, not temporal life, at the point of salvation (John 6:47; 10:27, 28; Romans 6:23; Hebrews 5:8, 9; 9:12).
according to the promise
The words “according to the promise” are the emphatic words of this verse. Just as Abraham received eternal life by faith, so we receive eternal life by claiming God’s promise of salvation. We are one with Old Testament believers.
The promise of grace made to Abraham (Ga 3:16,17) comes alike to anyone who trusts Christ’s cross for salvation. No one can work his way to heaven. All must come the same way – by God’s pure, unadulterated, sovereign grace.
God gives us eternal security at the point of our salvation.
God makes us secure in Christ because salvation depends on His power, not ours (John 10:29; Romans 8:31-32, 38,39) and on His promises (John 3:16-36; 5:24). God’s love (Romans 5:6-10) and immutability guarantee our eternal security (2 Timothy 2:12,13). He has the power to eternally deliver salvation for us (John 10:29; Romans 8:31-39). He preserves it for us (1 Peter 1:4,5; Jude 1, 24). He will never condemn the Christian to hell (Romans 8:1; Ephesians 1:3; 2:6) because our Defense Attorney defends our case (Hebrews 9:24; 7:25; 1 John 2:1,2). The indwelling Holy Spirit seals our salvation for eternity (Ephesians 1:13,14; 4:30).
Our verse says that it is impossible to become unborn once we are born spiritually (Galatians 3:26). God will complete His work of salvation in us (Philippians 1:6; Hebrews 12:2). It does not depend on us but upon Him.