If "God is love" why is he wrathful?

When we read in passages such as Exodus 20:5, that God is “jealous,” we are to understand divine jealousy in a Trinitarian way. The Father yearns for the dignity of the Son and Spirit, such that he is angry at anything and anyone who slights them. The Son is likewise passionate for the honor of his Father and the Spirit, and the Spirit burns with zeal for the respect of the Father and Son. Love, at the most sublime level, is the ardent regard each divine person has for the members of the godhead.  As such, God's communal love necessarily involves antipathy for idolaters who defame the Trinity by their sinful substitution of creation for Creator. But it is the effulgence of divine love which also brings sinners back into communion in the life of the Trinity, through redeeming grace. 

The Wrath of Man will Praise Him

"Surely the wrath of man shall praise you; the remnant of wrath you will put on like a belt." (Psalm 76:10)

The wrath of man is sometimes perplexing. We do not see how God's justice can be upheld when so much evil is done in the world. At the judgment, however, all eyes will be made to see how even ungodly rage redounds to the praise of God. The intricacies of a trillion historical plot lines will then come together to reveal God's overruling power, turning all things to good for those who love him. For now, we take solace in Biblical examples such as that in the book of Esther, where Haman's rage becomes the catalyst for God to bless his people and make his name great. For now, we wait and trust.