I was reading Hebrews’ comparison of Moses and Christ (Heb. 3:1-6) when I found the following helpful comments by Raymond Brown in his commentary on Hebrews (note: this is not the same Raymond Brown who has written Roman Catholic works and commentaries).
Right before these comments, Brown noted the great balance in Hebrews between the believer’s promised security and his necessary perseverance. Here are Brown’s comments on Hebrews 3:6:
First, the believer’s security is assured. Christians will not fail if they look dependently to their merciful and faithful high priest. So many temptations and pressures, insidious as well as blatant, can lure us away from Christ and the faith we profess. This epistle seems to demand so much from us in relentless pilgrimage, strenuous running and persistent continuance, but that is only part of its message. Time and again its firm truths sound out with ringing certainty: ‘He is able to help.’ ‘We are his house.’ ‘We share in Christ.’ ‘We have a great high priest.’ This is the ground of our confidence. We do not place our hope in what we do, but what he has done. Believers do not rely on what they are; that would be a religion of merit. They base their entire spiritual confidence on what he is.”
“Secondly, the believer’s continuance is essential. It is important to recognize the seriousness of this letter when it rightly insists on perseverance. F. F. Bruce describes this persistent endurance as ‘the test of reality’. There is no casual easy-going presentation of Christianity in these chapters. William Manson is perfectly right when he insists that to the author of this epistle, Christianity is ‘not a matter only of repenting and obtaining forgiveness, but of irrevocable commitment of life to a supernatural end.’ We are certainly in God’s house by faith in Christ but, to be real, that belief must be something more than the occasionally faltering faith which initially takes hold of Christ, or that excited faith which, with adoring gratitude, first renounces sin and comes to Christ for liberating pardon. It is hardly that vacillating faith which calls out in moments of bewildered dejection: ‘I believe; help my unbelief!’ It is a persistent faith which holds fast to its boldness and rejoices in the certain hope of better things. True Christian confidence is unwavering faith in a trustworthy God. He who has promised to keep us is eternally faithful and will not disappoint his people, but that truth is not meant to encourage careless complacency.”