“[…] indeed God who will justify the circumcised by faith and the uncircumcised through faith is one”, (Romans 3: 30).
Because two different words are used by Paul we can assume there is a reason for the change. The Greek word for “by” is “ek”, meaning “from out of”; on the other hand, the Greek word for “through” is “dia” and signifies “arising from, through, by means of”.
Clearly we are not speaking here of fleshly circumcision but of spiritual circumcision, as it is written: “But he is a Jew who is one inwardly; and circumcision is that which is of the heart, by the Spirit, not by the letter,” (Romans 2: 29). Justification of the circumcised in the heart by faith means, therefore, that those who already possess the faith will be justified on account of it, or because of it, hence: “out of it”.
On the other hand, those who are uncircumcised in their hearts will eventually be justified by having their faith tried, and tested. Since “without faith it is impossible to please [God]” (Hebrews 11: 6), the development of this faith-in-the-Creator in those uncircumcised in the heart must occur, if they are to be justified and deserve life in God’s kingdom for which Christians were taught to pray.
To justify the unbelieving through the acquisition of faith will be the work of Christ and his followers in the Millennial reign. As a result the earth will be filled with the knowledge of God (Habakkuk 2: 14), and “I will put My law within them…And they shall not teach again, … saying, ‘Know the Lord’, for they shall all know Me, from the least of them to the greatest of them, declares the Lord, for I will forgive their iniquity, and their sin I will remember no more,” (Jeremiah 31: 33, 34).