Acts records three times in gospel explanations that Jesus hung on a tree (Acts 5:30; 10:39; 13:29). Why speak of a tree? Why refer to the material of the cross instead of the cross itself?
Luke likely wanted his readers to assume that Peter and Paul explained in full what Luke had recorded in short. The mention of a tree would recall Deut 21:22–23, and, assuming the tree was explained as it was in Gal 3:10–14 and 1 Pet 2:24, perhaps Deut 27:26 and Lev 18:5 were recalled as well.
Consider Deut 21:22–23: “And if a man has committed a crime punishable by death and he is put to death, and you hang him on a tree, his body shall not remain all night on the tree, but you shall bury him the same day, for a hanged man is cursed by God. You shall not defile your land that the Lord your God is giving you for an inheritance” (ESV).
Deut 21:22–23 taught that, for criminals who died in a tree as a means of capital punishment (perhaps by noose, or, in Christ’s case, crucifixion), the criminal was cursed by God. But what is this curse?
Galatians 3:10–14 answers this question: “10 For all who rely on works of the law are under a curse; for it is written, ‘Cursed be everyone who does not abide by all things written in the Book of the Law, and do them.’ 11 Now it is evident that no one is justified before God by the law, for ‘The righteous shall live by faith.’ 12 But the law is not of faith, rather ‘The one who does them shall live by them.’ 13 Christ redeemed us from the curse of the law by becoming a curse for us—for it is written, ‘Cursed is everyone who is hanged on a tree’— 14 so that in Christ Jesus the blessing of Abraham might come to the Gentiles, so that we might receive the promised Spirit through faith” (ESV).
Gal 3:10 quotes Deut 27:26 to promise a curse to those who do not perfectly obey the Law. On the other hand, Gal 3:12 quotes Lev 18:5 to promise life to those who obey the Law’s commandments. In being contrasted with life that comes to the obedient, the curse is thus death for the disobedient—a death that is physical, spiritual, and eternal. The curse implies the absence of faith and thus the righteousness of God (Gal 3:11). The curse also implies the absence of the Spirit (Gal 3:14). The curse, then, is death to the one who disbelieves and disobeys God.
Assumed in Gal 3 is that no one perfectly obeys the Law and that all are therefore under this curse (cf. Gal 3:10). Thankfully, we find in Gal 3:13 that our sinless Christ was cursed for us by dying on the tree to redeem us from this curse. He lived a life of perfect obedience to the Law and then died a death that He did not deserve for those who indeed deserved it. By faith in Him, we find our curse removed and receive the Spirit, righteousness, and life (Gal 3:14).
Peter teaches the same truths in mentioning the tree as well. “He himself bore our sins in his body on the tree, that we might die to sin and live to righteousness” (1 Pet 2:24 ESV). 1 Pet 2:24 teaches that the purpose for Christ dying on the tree was to bear our sins, and that, by believing in Him, we would die to sin and live to righteousness.
So why mention the tree and not the cross? To speak of the tree recalled the curse of death for breaking God’s Law, and all deserve this curse because everyone has broken God’s Law (cf. Deut 21:22–23; 27:26). But Christ did not sin and did not deserve the tree. He deserved life for perfectly obeying the Law (cf. Gal 3:12). In dying such a death, then, He was able to take the curse of the Law upon Himself for others who had sinned (cf. Gal 3:13; 1 Pet 2:24a). When these sinners place their faith in Him, they find the curse removed and receive life and righteousness instead (cf. Gal 3:11, 14; 1 Pet 2:24b).
By recalling the tree, so also would one recall a trail of gospel truths. Praise God for sending Christ to die on the tree!