A.T. Robertson Commentary Acts 5:38

"And now I say unto you, Refrain from these men, and let them alone: for if this counsel or this work be of men, it will be overthrown:" — Acts 5:38 (ASV)

Refrain from (αποστητε απο). Second aorist (ingressive) active imperative of αφιστημ of verse 37. Do ye stand off from these men. "Hands off" was the policy of Gamaliel.

For if--be (οτ εαν--η). Hοτ gives the reason for the advice. Gamaliel presents two alternatives in terms of two conditional clauses. The first one is stated as a condition of the third class, εαν with the present subjunctive η, undetermined with prospect of determination. Assuming that it is from men, "it will be overthrown" (καταλυθησετα, first future passive of καταλυω, to loosen down like a falling house) as was true of the following of Theudas and Judas the Galilean.