Albert Barnes Commentary Jeremiah 42:20

"For ye have dealt deceitfully against your own souls; for ye sent me unto Jehovah your God, saying, Pray for us unto Jehovah our God; and according unto all that Jehovah our God shall say, so declare unto us, and we will do it:" — Jeremiah 42:20 (ASV)

Ye dissembled in your hearts - Or, “you have led yourselves astray,” that is, your sending me to ask counsel of God was an act of self-delusion. You felt so sure that God would direct you to go into Egypt, that now that He has spoken to the contrary, you are unable to reconcile yourselves to it.