Grace is confusing!

I have been thinking a lot about grace over recent months and have come to the decision that grace is so hard to fathom and grasp. With some people when you talk of grace they instantly go on the defensive saying that preaching grace gives people license to sin and doesn't give the call that people need to walk in holiness. Others radiate a smile and seem to blossom as you talk of grace - they send out this radiant smile as they realise the depth of their sin and bigness of God's grace and the depths He went to for them. The contrasts are startling! The contrasts are extreme - from serious caution, to awesome, uninhibited rejoicing - but yet both people are saved, both love Jesus, both have a relationship with God - it confuses me!?!?!...........