"Be sure thy sin will find thee out"
Public DomainBible

Miss Brent is quoting the Bible:

And Moses said unto them, If ye will do this thing, if ye will go armed before the LORD to war, And will go all of you armed over Jordan before the LORD, until he hath driven out his enemies from before him, And the land be subdued before the LORD: then afterward ye shall return, and be guiltless before the LORD, and before Israel; and this land shall be your possession before the LORD. But if ye will not do so, behold, ye have sinned against the LORD: and be sure your sin will find you out.

Numbers 32:20-23