There are at least three areas in life where people make a difference in social standing or in religious priority. They are (1) Jew and Greek, (2) bond and free, and (3) male and female.
The first area of division is cultural. The Jews in biblical times had no dealings with the Gentile nations. In fact, God told them not to mimic the Gentile nations as to their way of life. They were not to marry them or to have business dealings with them. This, of course, was sanctioned by God only to show his selection of Israel as a nation and his sovereign choice as it stands in his attributes--God can choose what or whom he will choose. Then Jesus broke the barrier when he spoke to the Samaritan woman in John chapter four. Then he completely eliminated the difference when he gave the Great Commission to his churches, that they should go and preach the Gospel to all nations (Matt. 28:18-20; Mark 16:15, etc.). Paul tells us in Romans 10:12 For there is no difference between the Jew and the Greek; for the same Lord over all is rich unto all that call upon him. In the local church of the Lord Jesus Christ there is no difference between the members in God's sight. They are all sinners saved by grace and baptized into the membership of that church (1 Cor. 12:13) whether they be Jews or Gentiles.
The second area of division is societal. There were both bond and free men in Bible times. The bondage of a slave did not preclude his being saved by the grace of God without the deeds of the law. The free man had no more opportunity to be born again than the bondman did. Paul was a free Roman, and he used that to his advantage; but he was not any more prone to be born again than a man who was in bondage. In the local churches in Galatia, the members were all saved by grace and baptized into the membership of those churches (1 Cor. 12:13) whether they be bond or free.
The third area of division is gender. There is neither male nor female. Now, there certainly is a vast difference between a male and a female in this life, but there is no difference in God's sight in salvation, and there is no difference in the membership of a local church. Certainly, in the churches there are different positions for male and female; but as far as membership itself, there is no difference in male and female.
We have now only to consider the reason that the divisions are not different. It is because of what is mentioned in verse 29: "And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise." It is, of course, because in Christ we are all the children of Abraham (his seed) and heirs of Abraham. Rom. 2:29 But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God. We are joint-heirs with Christ: Rom. 8:17 And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together.
So, there is no difference in any of these areas; therefore, we are all personally responsible to God no matter what nationality, social standing, or gender. Every man must give account of himself to God (Romans 14:12); and in the churches we are to love one another, for there is not one member that is any better than another member as far as our standing before God.