Christians are Christians by virtue of certain acts of God which took place at a definite time in the past, but these acts of God have released a dynamic force which will never allow Christians to stick fast at any point short of that divine rest which in this life is always a goal to be aimed at and never a stage which has been reached. The faith once for all delivered to the saints is not something which can be caught and tamed; it continually leads the saints forth to new ventures in the cause of Christ, as God calls afresh. It was Abraham’s firm faith in the unchanging God that made him so ready to go forth at God’s bidding, not knowing whither he might be led. To stay at the point to which some revered teacher of the past has brought us, out of a mistaken taken sense of loyalty to him; to continue to follow a certain pattern of religious activity or attitude just because it was good enough for our fathers and grandfathers—these and the like are temptations which make the message of Hebrews a necessary and salutary one for us to listen to. Every fresh movement of the Spirit of God tends to become stereotyped in the next generation, and what we have heard with our ears, what our fathers have told us, becomes a tenacious tradition encroaching on the allegiance which ought to be accorded only to the living and active word of God. As Christians survey the world today, they see very much land waiting to be possessed in the name of Christ; but to take possession of it calls for a generous measure of that forward-looking faith which is so earnestly urged upon the readers of this epistle. Those first readers were living at a time when the old, cherished order was breaking up. Attachment to venerable traditions could avail them nothing in this situation; only attachment to the unchanging and onward-moving Christ could carry them forward and enable them to face a new order with confidence and power. So, in a day when everything that can be shaken is being shaken before our eyes and even beneath our feet, let us in our turn give thanks for the unshakable kingdom which we have inherited, which endures forever when everything else to which men and women may pin their hopes disappears and leaves not a wrack behind.
—F. F. Bruce, The Epistle to the Hebrews (NICNT)