I posted these in a comment to somebody, and thought they might be worth sharing:
The best analogy I can think of to the Catholic understanding of salvation — and this has made all the difference in my life and in my Christian walk — is that we are trapped in our sins at the bottom of a pit, and entirely unable to do anything on our own to get out of it. Then God lowers us a rope (grace), and by that rope He can pull us out. But first we have to take the rope.
Another one is this: we are little children taking our first steps — or alternately, we are old and decrepit, or in rehab — in any case, we can’t walk on our own. We can’t even take the first step under our own power. But Christ takes hold of us (by His grace), and as long as we hold on to Him, He holds us up. If we let go even for an instant, or try to do anything without Him, we go tumbling. But as long as we let Him hold us and help us, we are able to take steps forward. He is the one doing all the heavy lifting — we are just moving our feet, inching slowly toward our sanctification. (The old and decrepit person may work better, because unlike the child, we’ll never have the strength to walk on our own. The only good thing about the child metaphor is the paternal aspect.)