Nobody cares about the speaker of "I Am" anymore. He's been completely abandoned. As if we couldn't guess how terrible this is, the speaker spends a good part of the poem telling us all about it: he's tossed aside like some vapor, nobody cares about him, nobody knows who he is, and on and on. The speaker feels so bad, in fact, that he in turns wants to abandon the world forever. And you thought you had it bad. Sheesh!
Abandonment is a way of dehumanizing somebody. For example, the speaker's friends treat him like he's not even a real person anymore, just a forgotten memory. Sad, right?
Religion is one sure-fire way to cure loneliness. The speaker's seeks to solve his abandonment by getting next to God.