The Magi are the the wise men from the East who in the traditional story of Jesus birth came bearing gifts of gold, frankincense, and myrrh. The use of the word magi is a biblical allusion to these men because they brought gifts appropriate for a promised king. When they arrived, the found Jesus wrapped in cloths, lying in a manger, and born in a stable. These were certainly conditions for a most impoverished person.
These magi are significant because they help create many parallels to the story of Jim and Della. Both Jim and Della sacrifice something most important to themselves to give the other a gift of great significance and honor. The concepts of sacrifice and appropriateness are both relevant in the Jesus story and the story of Jim and Della.