25 whom God set forth as a propitiation by His blood, through faith, to demonstrate His righteousness, because in His forbearance God had passed over the sins that were previously committed,
In Romans 3:24-25 Paul pressed into service the notions of law (justification), freedom from the slave market (redemption), and in this verse the tabernacle or temple (mercy-seat, propitiation) to give a striking picture of our salvation in Christ. God declared us as right as He is right, gave us liberty to relate to Him, and made it known publically that He was satisfied about our salvation (propitiation).
25 whom [Christ] God set forth [offered publically]
“Set forth” carries the idea of to present, to purpose. Literally it means to place before so as to be manifest. The Father put Jesus’ death before the public. God hid the Old Testament mercy seat (the place of propitiation) from view of the general public (only the high priest was able to observe it). In contrast to that, He presents publically the sacrifice of Christ for all to see. God is righteous in all that He does.
God made it possible, for anyone willing, to see what He did about our sins.
God had a place where He displayed His mercy in the Old Testament (the mercy seat), but now God displays His mercy in a new manner—Christ on the cross suffering for our sin. Before Christ, God hid the mercy seat in seclusion in the Holies of Holies, but with Christ the sacrifice, He made it a public affair. Contemptuous crowds watched the crucifixion out in the open.
God made it possible for anyone with positive volition to see what He did about our sins—that is, He sent Jesus to pay for our sins.