Symbolism, Imagery, Allegory
One of the first major flashing neon-sign style symbols we see in this book is the cruciform (or "cross-shaped") tree that Father Latour stumbles across while he's lost in the New Mexico desert. Yep. Just count the Biblical references in that statement.
Well, there are actually only really two, but hoo-boy are they biggies. The number one is the dang cross shape. The major symbol of Christianity, guys. Father Latour would have very much believed that Christ died on the cross for our sins.
Seeing this tree is a big moment of revelation for Latour. If Christ was crucified for the good of mankind, then Latour reasons that the very least he can do for the people of New Mexico is suffer through the wilderness and learn to love his adopted homeland.
You also have a Hebrew Bible shout-out: Moses wandered into the wilderness, saw a crazy burning bush, and had God tell him to lead the Israelites out of bondage in Egypt and into freedom. Huh. Latour also is in the (New Mexico) wilderness, and he also sees a crazy plant. So maybe—just maybe— it's time for him to lead the people of New Mexico toward (what Latour would have believed as) the truth of Catholicism. You know, cause the truth will set you free.
So Latour's wandering in the desert, followed by ye olde cruciform tree, is a double-whammy of Biblical symbolism. But both arms of this symbol tell us readers (and Latour) the same thing: suffer through New Mexico and you will be given divine guidance.
When Latour sees the cruciform tree, he's figuring that he might die of thirst out in the brutal heat. As the narrator tells us:
It was not a thick-growing cone, but a naked, twisted trunk, perhaps ten feet high, and at the top it parted into two lateral, flat-lying branches, with a little crest of green in the centre, just above the cleavage. Living vegetation could not present more faithfully the form of the Cross. (1.1.4)
Father Latour is looking for any help he can get, so he jumps off his horse and kneels in front of this tree, praying for God to help him. And sure enough, his horses smell water soon afterward and lead him to the house of a Mexican family living nearby. These people treat Latour like gold and give him everything he needs, so Latour decides that God must really be looking out for him in this strange, harsh new land.