Paul introduces a shift in the discussion that contrasts in a very marked way with what he was saying before. The contrast is between a time of sin and condemnation and a new reality, the “now” of salvation history inaugurated by Jesus. The previous time was described by Paul as a time when Jews and gentiles demonstrated to be in a state of sin, totally unable to live a righteous life. They were all condemned before the bar of God.
The “now” is the time when God did something wonderful for the human race. He revealed to us a new way of salvation that is absolutely independent from the law, and yet the law and the prophets testified about it; a righteousness of God carefully defined by Paul as the “righteousness of God by faith in Jesus Christ.” He is carefully stating that there is no other form of righteousness that could solve the human predicament except the righteousness that is by faith in Jesus available to all/everyone who believes. Notice the use of “all” in the sense of “everyone.”
The phrase “for/because there is no difference/distinction” is used to establish the fact that when it comes to salvation God saves all human beings, that is to say Jews and gentiles, in the same way, namely, through faith in Jesus (“all who believe”).