The very last line of Bless Me, Ultima warrants a bit of exploration. Ultima has blessed Antonio, she has died, and he has buried her owl under the forked juniper tree just like she asked him to. He reflects on the Catholic burial rites that will soon come for Ultima. Then, he finishes the novel with this:
But all that would only be the ceremony that was prescribed by custom. Ultima was really buried here. Tonight. (22.277)
In those final lines, Antonio comes to some conclusions he's been moving toward the entire book. He knows that his mother will bury Ultima in the proper Catholic fashion, but he now comes to realize that the act is merely "custom." Ultima belonged to another faith—another set of beliefs, and that's what he chooses to pay tribute to.
In burying the owl, Antonio suggests that "Ultima was really buried here." This demonstrates another strong acceptance on Antonio's part. He believes in the connection between Ultima and the owl, and he's fulfilled Ultima's dying wish to bury the owl under the juniper tree. He won't deny the Catholic custom that's coming down the pike, but he will respect the folk custom that Ultima has asked him to undertake, too. In a way, this moment serves to show that Antonio has embraced much of what Ultima taught him, while still maintaining a grip on the traditions he was raised in as well.