New Defender's Study Bible Notes
2:7 letteth. The Holy Spirit, through the true Church, “letteth” (that is, delays, or hinders) the revelation of the son of perdition. In effect, He will be “taken out of the way” when all those He indwells and guides are caught up to meet the Lord. Of course, since He is omnipresent, He will still be present and working on earth, though not through the Church.
2:7 let. The English word “let” is derived from the Old English laetan, which in turn came from the ancient Teutonic. Our modern word “late” is from the same source, the original meaning of laetan being “to make late” or “delay.” Thus, this word, as used in this verse, meant “make late” or “delay.” By a strange permutation of language meanings, it has in more recent times come to mean “permit,” almost the opposite of its original meaning.