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, ESV
What if God only wanted to be just? Would there be anything wrong on his end if he decided to not play the role of the justifier? Not at all. He very well could have only punished sin and not rescued the sinner, and he would have been completely just in doing that.
But he didn't.
God's grace toward us and his love for us is seen in the fact that God also wanted to be the justifier. We are the recipients of his desire to justify sinners, for all have sinned and fall short of the glory of God, and are justified by his grace as a gift, through the redemption that is in Christ Jesus, whom God put forward as a propitiation by his blood, to be received by faith (Romans 3:23-25a, ESV).
To only be just God must punish sin. However, to be the justifier of souls, he must punish sin using another target for his wrath and punishment for our sin (propitiation) so that he might extend grace and mercy to us—the ones who brought about sin in the first place.
It is because God wanted to justify sinners that he came for us, as Jesus, to become the new target of the wrath of God so that he might extend grace and mercy to us. And as we place our faith in Christ, we are justified and made right with God because of that punishment that Christ endured on our behalf. And all of this is God's gift to us.
God is just. God is also the justifier.
Wow. Let that sink in and I'm sure you'll say the same thing.