A.T. Robertson Commentary Acts 23:21

"Do not thou therefore yield unto them: for there lie in wait for him of them more than forty men, who have bound themselves under a curse, neither to eat nor to drink till they have slain him: and now are they ready, looking for the promise from thee." — Acts 23:21 (ASV)

Do not therefore yield unto them (Συ ουν μη πεισθηις αυτοις). First aorist passive subjunctive of πειθω, common verb, here to be persuaded by, to listen to, to obey, to yield to. With negative and rightly. Do not yield to them (dative) at all. On the aorist subjunctive with μη in prohibitions against committing an act see Robertson, Grammar, pp. 851-4.

For there lie in wait (ενεδρευουσιν γαρ). Present active indicative of ενεδρευω, old verb from ενεδρα (verse 16), in the N.T. only here and Lu 11:54 which see.

Till they have slain him (εως ου ανελωσιν αυτον). Same idiom as in verse 12 save that here we have ανελωσιν (second aorist active subjunctive) instead of αποκτεινωσιν (another word for kill), "till they slay him."

Looking for the promise from thee (προσδεχομενο την απο σου επαγγελιαν). This item is all that is needed to put the scheme through, the young man shrewdly adds.