Mercy without justice is meaningless.  Justice without mercy is cruel.  The first instance of God's mercy is in Genesis 3 when He administered His divine justice to the participants of that first and only incident in Eden:  Adam, Eve and the snake.  He cast Adam and Eve out of paradise, made them mortal, caused Eve to endure pain during childbirth, turned Adam into a beast of burden and condemned the snake to slither on its belly and forced to eat dust forever.  He also promised a Savior, born of the seed of a woman (virgin birth) who would bruise the head of the snake's spawn and show the banished children of Eve the way to eternal life.