5 Then they said to Jeremiah, “May the LORD be a true and faithful witness against us if we do not act in accordance with everything the LORD your God sends you to tell us.

Read Jeremiah 42:5 Using Other Translations

Then they said to Jeremiah, The LORD be a true and faithful witness between us, if we do not even according to all things for the which the LORD thy God shall send thee to us.
Then they said to Jeremiah, "May the LORD be a true and faithful witness against us if we do not act according to all the word with which the LORD your God sends you to us.
Then they said to Jeremiah, “May the LORD your God be a faithful witness against us if we refuse to obey whatever he tells us to do!