“It was to show his righteousness at the present time, so that he might be just and the justifier of the one who has faith in Jesus.” -Romans 3:26
“At the present time” should be understood in relation to “passed over former sins” in the previous verse.
It now being established by Paul’s argument that the whole human race is condemned for injustice, and God alone has the honor of being just. Though God is merciful in delaying judgment on sins past, he is not merely merciful; he is also gracious and does not hold back the riches of his righteousness for himself alone but demonstrates the fullness of his righteousness now (at Christ’s revelation) by luring forth his righteousness to all men who have faith in Jesus.
And in being the “justifier of the one who has faith in Jesus,” he does not compromise his own integrity to do it. That is, he remains just because he has executed the Divine Wrath which was due compensation for those “former sins” upon Jesus.
The German Reformer, Martin Luther, called this “the Great Exchange.”