A.T. Robertson Commentary John 12:41

"These things said Isaiah, because he saw his glory; and he spake of him." — John 12:41 (ASV)

Because he saw his glory (οτ ειδεν την δοξαν αυτου). Correct reading here οτ (because), not οτε (when). Isaiah with spiritual vision saw the glory of the Messiah and spoke (ελαλησεν) of him, John says, whatever modern critics may think or say. So Jesus said that Abraham saw his day (8:56). Cf. Hebrews 11:13.