Grace-

a) the freely given, unmerited favor and love of God.
b) the influence or spirit of God operating in humans to regenerate or strengthen them.
c) a virtue or excellence of divine origin: the Christian graces.
d) Also called state of grace. the condition of being in God’s favor or one of the elect.

There is a really good blog post over at DesiringGod.org by Paul Tripp, pastor of Tenth Presbyterian Church in Philadelphia. Here is an excerpt-

“So grace is a story and grace is a gift. It is God’s character and it is your only hope. Grace is a transforming tool and a state of relationship. Grace is a beautiful theology and a wonderful invitation. Grace is a life-long experience and a life-changing calling. Grace will turn your life upside down while giving you a rest you have never known. Grace will require you to face your unworthiness without ever making you feel unloved.”