Hebrews 3:15

ἐν τῷ λέγεσθαι. “While” or “since it is said.” It is better to give this sense to the phrase than to suppose a long parenthesis between this verse and the φοβηθῶμεν οὗν of Hebrews 4:1 (which is the view of the construction taken by Chrysostom and other Greek fathers); or to join it to the παρακαλεῖτε ἑαυτοὺς of Hebrews 3:13.

μὴ σκληρύνητε. Some editors mistakenly supposed that σκληρύνητε was a pres. subj., which would involve a solecism. It is an aor. subj. (ἐσκλήρυνα).