I got this in my Catholic Catechism email. Just copy/pasting to here, because it’s so clear, simple and very worthwhile.
Can someone earn heaven by good works?
No. No man can gain heaven merely by his own efforts.
The fact that we are saved is God’s grace, pure and simple, which nevertheless demands the free cooperation of the individual.
Although it is grace and faith through which we are saved, nevertheless, our good works ought to show the love produced by God’s action in us.
Are we all supposed to become “saints”?
Yes. The purpose of our life is to be united with God in love and to correspond entirely to God’s wishes.
We should allow God “to live his life in us” (Mother Teresa). That is what it means to be holy: a “saint”.
Every man asks himself the question: Who am I and why am I here, how do I find myself?
Faith answers: Only in holiness does man become that for which God created him. Only in holiness does man find real harmony between himself and his Creator.
Holiness, however, is not some sort of self-made perfection; rather, it is union with the incarnate love that is Christ.
Anyone who gains new life in this way finds himself and becomes holy.
Corresponding Catholic Catechism section (sections 2006-2029) and other references @ http://www.catholiccrossreference.com/catechism/#!/search/2006-2029