A.V. gives diligently as the force of ἐπὶ; but ἐπὶ signifies direction rather than intensity. The idea is exercising oversight. Only here and 1Pe 5:2.
Fail of (ὑστερῶν ἀπὸ)
Rend. “fall back from,” implying a previous attainment. The present participle marks something in progress: “lest any one be falling back.”
Root of bitterness (ῥίζα πικρίας)
From lxx, Deu 29:18. A bad man in the church. Ῥίζα of a person, 1 Macc. 1:10.
Springing up (ἄνω φύουσα)
The participle pictures the springing up in progress; the root gradually revealing its pernicious character.
Trouble (ἐνοχλῇ)
Only here and Luk 6:18, see note.
Many be defiled (μιανθῶσιν οἱ πολλοί)
Rend. “the many”: the majority of the church. For the verb see on Joh 18:28.