Rime of the Ancient Mariner

This is the first time I've read the Rime of the Ancient Mariner and I actually read and listened to it at the same time.  This helped me because I had no idea what the poem was about, so the audio helped with the emphasis of the words and the way it rhymed.

The line (or stanza) that I liked the best out of the whole poem was:

402 "The spirit who bideth by himself
403 In the land of mist and snow,
404 He loved the bird that loved the man
405 Who shot him with his bow."

I wrote about this in the discussion board on Blackboard -- This to me symbolizes the love of God and His forgiveness of sin.

So, there's this spirit that comes down upon the Mariner and the boat when the Albatross was shot by the Mariner's bow.  As every sea-faring person should know, killing an Albatross is bad luck for the ship and its mates.  So why did the Mariner shoot and kill the bird?  This bird could be all of the good things we have in life, and the sin that affects it (the crossbow).  I read about it in someone else's post on discussion board, and she said that sometimes even when we know we are committing a sin, we don't think about its repercussions.  This is what the Mariner went through -- consciously doing something real bad and not thinking about the outcome.

I'll post what I wrote about in the discussion board here, too, because I can't explain it any better than I did on there:

"This to me describes the love of God [the spirit] in the form of the Albatross. The bird [or spirit, the same in one] still loves the man even though the man [the Mariner] "shot him with his bow." This relates to rejecting God and his guiding presence at times when one thinks that they are in complete control of their circumstances. Even though you may reject the presence of God, that doesn't mean that he doesn't love you anymore.

"By killing the bird it makes the bird more tangible because first, it falls down and the Mariner wears this bird (or burden) around his neck, and second because the Mariner can understand it better by it being tangible and not in the sky flying freely. But does this help him with getting to land any faster? No, because he needs to believe that the spirit, even though it is not there anymore, will take him home. The Holy Spirit is notpresent in a tangible way. This is why faith in what one believes is the guiding force of a lot of decisions and pathways.

"I just realized this, but, the bird around the Mariner's neck could symbolize his crosses (his burdens and troubles) that he carries, just as Jesus did for us. He just had to realize to give up all his troubles and worries and lift them up to God."

In the lines before 402, it says:

398 'Is it he?' quoth one, 'Is this the man?
399 By him who died on cross,
400 With his cruel bow he laid full low
401 The harmless Albatross.

I'm kind of confused with line 399 ... who is or what does it mean by "by him who died on cross"?  I know it directly references Jesus dying on the cross...but is the spirit describing the Mariner as the one who "helped" in the crucifixion?  If it is, then the Mariner did help the act of crucifying Jesus, aka the Albatross.  They were both harmless creatures, only here to help and guide and not to be negative influences on us.