John Gill Commentary Jeremiah 7:8

"Behold, ye trust in lying words, that cannot profit." — Jeremiah 7:8 (ASV)

Behold, you trust in lying words
What they are dissuaded from, (Jeremiah 7:4), is here affirmed they did, and which is introduced with a note of asseveration, attention, and admiration; it being a certain thing that they did so; and was what was worthy of their consideration and serious reflection upon; and it was astonishing that they should, since so to do was of no advantage to them, but the contrary: that cannot profit ; temple worship and service, legal sacrifices and ceremonies, could not take away sin, and expiate the guilt of it; or justify men, and render them acceptable to God; these, without faith in the blood and sacrifice of Christ, were of no avail; and especially could never be thought to be of any use and profit, when such gross abominations were indulged by them as are next mentioned.