Before the skins were taken from the animals, the lambs were undoubtedly sacrificed. They were killed and their blood was shed. I believe that God probably killed the lambs in the presence of Adam and Eve and that they witnessed the sacrifice. It must have given them a deep impression. Perhaps Adam said to Eve, "Eve, don't you know that that should be our destiny? We should be killed. Our blood should be shed because we fell, committed sin, and transgressed God's prohibition. According to God's prohibition, we should be killed. But God didn't kill us, Eve. God is killing these lambs in our place. How thankful and grateful we should be to these lambs. They are our substitute."
One day the Lord Jesus came, and John the Baptist said of Him, "Behold, the Lamb of God" (John 1:29). John 1:29 is a development of Genesis 3:21. In type, when the lambs were slain, Christ had already been slain in the eyes of God, for He was slain from the foundation of the world (Rev. 13:8). Hebrews 9:22 says, "Without shedding of blood there is no forgiveness." Thus, this matter of shedding of blood was also sown as a seed in Genesis 3:21 and is developed in John 1:29 and Hebrews 9:22. If you read the Epistles in the New Testament, you will notice how many times the blood is mentioned. We have been redeemed by the precious blood of God's Lamb ordained by God for us before the foundation of the world (1 Pet. 1:18-20). Christ was ordained before Adam's fall. We can see a picture of the shedding of Christ's blood there in the garden. Without the shedding of blood, how can a righteous God justify sinful man? Without the shedding of blood, it would not have been legal, lawful, righteous, or fair for God to put a covering upon fallen man. However, before God covered sinful man with the coats of skins, God judged and killed him in the sacrifice. God will never kill us, because He has already killed us in Christ. On the cross Christ was killed by the righteous God. Thus, whenever we respond to the gospel and say, "Living," God immediately comes and covers us with Christ as our righteousness. This means that God's justification is based upon redemption. The putting on of the coats of skins was based upon the shedding of the blood of the sacrifice, for the sacrificial lamb was actually a substitute for sinful man.
Although many Christians talk about substitution, about Christ's having died in our place, not many realize the matter of union. However, genuine substitution is based upon union. Adam and Eve were sinful, and the lambs were killed and their blood shed for their sins. How could the killing of the lambs have been their killing? If the lambs and Adam and Eve had been separate from one another, the lambs could not have substituted for them. Once Adam believed in the glad tidings God covered him with a coat of the lamb skins, and he became one with the lamb. The sinner had become one with the substitute. This is union. Union brings about the effectiveness of substitution, for without union substitution stands alone. Substitution has nothing to do with us until we enter into that union. Once we participate in that union, whatever the substitute has accomplished is ours. Christ has done everything for us on the cross, but without union all that He has accomplished on the cross is unrelated to us. But if we say, "Amen, Lord," Christ will be put upon us, and we will be put into Christ. Since we are one with Christ, whatever Christ has accomplished on the cross becomes ours; it is our portion. Union brings in the effectiveness of substitution, and substitution is based upon union.
When we preach the gospel, some people always ask us, "As long as Christ has died for us on the cross, why do we need to believe? You have just told us that He has accomplished full redemption for us. Why then do we have to believe?" You need union. If you do not believe in Christ, you do not have this union. If you do not have union with Him, whatever He has done on the cross cannot be appropriated by you or applied to you. We need to believe in Christ. Whenever the Bible speaks about believing for salvation it uses the preposition "in." We must believe in Him. This little word "in" denotes union. To believe in Jesus Christ is to be one with Him, to have union with Him. If I am a poor man and you are a billionaire, you might be afraid to be united with me, but I would be glad to be joined with you, because once I am united with you everything you have is mine. This is why so many women want to marry rich men. According to California law, because of the union between husband and wife, whatever the husband has in his name also belongs to his wife. We have the best marriage. We, the poor beggars, have been married to Christ, the greatest billionaire. Whatever He has, whatever He is, whatever He has done and is going to do, whatever He has attained and obtained—everything is ours. We are now in Christ. This matter of union was also sown as a seed in Genesis, has been fully developed in the Epistles of the New Testament, and will ripen into a harvest in Revelation 21.