Complex sentence: The theology of angels, and tutelary spirits, has undergone many refinements since the 400s, and belief in both the East and the West is that guardian angels protect whichever person to whom God assigns them, cf. CCC 336.
Split into simpler sentences: The theology of angels and tutelary spirits has undergone many refinements since the 400s. Belief in both the East and the West is that guardian angels serve to protect whichever person God assigns them to, cf. CCC 336.