Adam Clarke on Hebrews 4:11

Let us labor therefore - The word σπουδασωμεν implies every exertion of body and mind which can be made in reference to the subject. Rebus aliis omissis, hoc agamus; All things else omitted, this one thing let us do. We receive grace, improve grace, retain grace, that we may obtain eternal glory.

Lest any man fall - Lest he fall off from the grace of God, from the Gospel and its blessings, and perish everlastingly. This is the meaning of the apostle, who never supposed that a man might not make final shipwreck of faith and of a good conscience, as long as he was in a state of probation.