Christ, the son of Abraham, brings us the divine blessing for us to inherit God. Galatians 3:29 says, "If you are of Christ, then you are Abraham's seed, heirs according to promise." Abraham's seed is only one, Christ (Gal. 3:16). Hence, for us to be Abraham's seed we must be of Christ, that is, a part of Christ. Because we are one with Christ, we are Abraham's seed, heirs according to promise, inheriting God's promised blessing, which is the all-inclusive Spirit as the ultimate consummation of the processed Triune God to be our portion.
Acts 26:18 refers to the believers' divine inheritance. This inheritance is the Triune God Himself with all that He has, all that He has done, and all that He will do for His redeemed people. This Triune God is embodied in the all-inclusive Christ (Col. 2:9), who is the portion allotted to the saints as their inheritance (Col. 1:12).
Ephesians 1:13 and 14 reveal that the Spirit is "the pledge of our inheritance." Since God is our inheritance, the Holy Spirit is the pledge of this inheritance to us.
In the Old Testament God made a covenant with Abraham (Gen. 12:2-3; 15:4-18; 17:1-2; 22:17-18) and also with David (2 Sam. 7:8-16). In order to understand how we may experience and enjoy Christ as the son of David and the son of Abraham, we need to consider these two covenants.
The covenant God made with Abraham concerned God's coming to be the blessing to His chosen people. This covenant is related to God's purpose in creating man. God made mankind to be His vessels to contain Him. God made man in His own image and after His likeness so that man could contain God, taking God as his life and life supply. For man to take God as his life and life supply is the greatest blessing in the universe. This is the enjoyment of the Triune God. However, due to the fall, this great blessing was lost by man.
Although man fell, God could not give up His eternal purpose. Satan's doings cannot annul God's purpose. The created race had fallen, but God continued working to fulfill His purpose by coming to a chosen race. The created race, the race of Adam, was a failure, so God came to another race, the chosen race, the race of Abraham. Whereas Adam was the head of the created race, Abraham was the head of the chosen race.
God made a covenant with Abraham, and this covenant concerns God's being the enjoyment and everything to His chosen people. Galatians 3:14 indicates that the New Testament is the fulfillment of the covenant God made with Abraham. In this fulfillment, the processed Triune God consummated as the all-inclusive Spirit is the blessing to God's chosen people. In the gospel, we have received the all-inclusive Spirit as God's consummation to be the life, life supply, and everything for our enjoyment. As a result of the covenant God made with Abraham, the processed Triune God as the consummated Spirit has become our enjoyment.
Galatians 3:29 tells us that because we are of Christ, we are Abraham's seed, heirs according to promise. What will we inherit? We will inherit the processed Triune God consummated as the all-inclusive Spirit. If we realize this, we will understand why Christ had to be the son of Abraham. Christ had to be the son of Abraham to fulfill God's covenant with Abraham so that God, after being processed, could be our blessing. Now for us to enjoy Christ as the son of Abraham means that we enjoy the Triune God promised to Abraham. This is a matter of blessing.