Practically all of the authoritative dictionaries today tell us that the conjunctions “as if” and “as though” are synonymous in the sense of “like something was actually so,” “as it would be if,” “as to suggest the idea that,” or “as would be true if.” Personally, though, I am stylistically partial to “as though” because I think it sounds more accepting of the stated presumption than “as if,” which seems to me to convey a somewhat weaker belief in that presumption.
IMAGE CREDIT: LEARNESL.NETFor this reason, I think your choice of “as though” for these two sentences of yours is perfect for their context: “Pray
as though everything depends on GOD. Work
as though everything depends on YOU.” It’s unmistakable that a believer in God is speaking here. In contrast, see what happens when “as if” in used instead for those two sentences: “Pray
as if everything depends on GOD. Work
as if everything depends on YOU.” Somehow, although both affirmative-sounding, these “as if”-using sentences seem to convey a hint of cynicism towards the stated presumptions.
This isn’t to say, though, that there are no contexts in which “as if” and “as though” are not perfectly equivalent. Consider the following three sets of examples:
“She rushed out of the house
as if goblins were chasing her.”
“She rushed out of the house
as though goblins were chasing her.”
“It looked
as if he had not slept all night.”
“It looked
as though he had not slept all night.”
“They looked at us
as if we were from another planet.”
“They looked at us
as though we were from another planet.”
I think you’ll agree with me that there isn’t any perceptible difference in meaning between the sentences in each of those pairs.