"Blackbird"

Yester-day, I finished reading the introduction to 1964: Eyes of the Storm.  Near the end, there's a quotation from "Blackbird," and I noticed an ambiguity in the line "You were only waiting for this moment to arise."  I don't know the proper grammatical terms necessary to explain this ambiguity precisely, but the main difference is whether it's "you" that's arising (where the arrival of "this moment" is a sort of prerequisite) or it's "this moment" that's arising (where "this moment to arise" is the direct object of the verb "waiting for").  Comparison with the later line "You were only waiting for this moment to be free," which has the same structure, suggests the former, but I think the latter is also grammatically viable.