* why do the mariners said the bird as a christian soul?

Dear Student!

In the initial part of the poem, we are told that the ship begins its journey though after some time, it is driven off its course towards the South by a strong storm. In the following paragrpahs, we come across references to snow. We are told that they could see nothing except snow all around themselves.

The albatross comes from no where and seems to guide them out of the waters of Antarctic. It is for this seeming good deed that the bird is referred to as "a Christian soul".

Hope this answers your question.

Best wishes!