A.T. Robertson Commentary Hebrews 10:38

"But my righteous one shall live by faith: And if he shrink back, my soul hath no pleasure in him." — Hebrews 10:38 (ASV)

If he shrink back (εαν υποστειλητα). Condition of third class with εαν and the first aorist middle subjunctive of υποστελλω, old verb to draw oneself under or back, to withdraw, as already in Ac 20:20,27; Galatians 2:12. See Ro 1:17 for the quotation also of "the just shall live by faith."