The thing to remember when you are comparing the OT to the NT, is that God is talking to two different men in each of the testaments. The OT was directed towards the fleshly man, especially in regards to the Law(Ten Commandments). The promise was given to Abraham's seed, but now, the promise is given to the inner man, that part of mankind that God saves.
Galatians 3
6 Even as Abraham believed God, and it was accounted to him for righteousness.
7 Know ye therefore that they which are of faith, the same are the children of Abraham.
8 And the scripture, foreseeing that God would justify the heathen through faith, preached before the gospel unto Abraham, saying, In thee shall all nations be blessed.
9 So then they which be of faith are blessed with faithful Abraham.
When we believe from the heart that Jesus is Lord, we then obtain that very same promise that was given to Abraham's seed. We become the "seed of Abraham" when we are born again/born from above. God does not have two promises for two seeds(natural Israel and the Church), but one promise to the one "seed", the believers.
Romans 6
17 But God be thanked, that ye were the servants of sin, but ye have obeyed from the heart that form of doctrine which was delivered you.
18 Being then made free from sin, ye became the servants of righteousness.
Just the above passage from Romans 6. When we obey from the heart, we become servents of righteousness. What is made righteous? The soul, the inner man, if you will. Our fleshly body will not be made righteous while we are alive here on earth. It must have a change take place, where the corruption puts on incorruption, the dishonorable is raised in honor, the weak is raised in power, IOW, in the resurrection. God looks at us inwardly, and not outwardly. He looks at our inner man, and if He see Jesus' blood, He sees us as being righteous, not of our own accord, but because of Jesus' righteousness.
Galatians 3
23 But before faith came, we were kept under the law, shut up unto the faith which should afterwards be revealed.
24 Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith.
25 But after that faith is come, we are no longer under a schoolmaster.
26 For ye are all the children of God by faith in Christ Jesus.
27 For as many of you as have been baptized into Christ have put on Christ.
28 There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus.
29 And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise.
i am I AM's!!
Willis