Romans 3:25 (HCSB)

God presented Him as a propitiation through faith in His blood, to demonstrate His righteousness, because in His restraint God passed over the sins previously committed.

  To propitiate means “to appease divine wrath.”  This is an inconvenient truth for people who do not like the penal substitutionary theory of the atonement.  I have no such qualms.  This best explains how God can be a righteous judge [not allowing sin to go unpunished] and the justifier of sinners.  Penal substitution in which Christ takes the wrath of God upon himself is a beautiful thing.