A Brief Word on God's Wrath by Leon Morris

"The general picture which the Old Testament gives us of God is of One who is by nature merciful, and who cannot be swayed by man's puny efforts. In the last resort forgiveness is always due to God's being what He is, and not to anything that man may do. Because God is God, He must react in the strongest manner to man's sin, and thus we reach the concept of the divine wrath. But because God is God, wrath cannot be the last word. 'The Lord is good; his mercy endureth for ever' (Ps. 100:5)." - p. 154, The Apostolic Preaching of the Cross, 3rd Revised Ed., Leon Morris