The "lost saints" aren't misplaced Catholic statues. Instead, they're the people you used to believe in that you don't have faith in anymore. You know, heroes who let you down, whether they're famous people (Roger Clemens? Britney Spears?) or just friends or family members who you once had a really high opinion of and now, well, they seem merely human.
So this kind of loving is also about faith: what if you could take the love you had for your heroes, before you were disillusioned about them, and channel that into loving someone? That's the kind of love the speaker is describing here.
This is the seventh kind of love mentioned in the poem, but who's counting?