“It is a striking likeness when he compares faith leaning on God’s word to an anchor; for doubtless, as long as we sojourn in this world, we stand not on firm ground, but are tossed here and there as it were in the midst of the sea, and that indeed very turbulent; for Satan is incessantly stirring up innumerable storms, which would immediately upset and sink our vessel, were we not to cast our anchor fast in the deep.
For nowhere a haven appears to our eyes, but wherever we look water alone is in view; yea, waves also arise and threaten us; but as the anchor is cast through the waters into a dark and unseen place, and while it lies hid there, keeps the vessel beaten by the waves from being overwhelmed; so must our hope be fixed on the invisible God. There is this difference, — the anchor is cast downwards into the sea, for it has the earth as its bottom; but our hope rises upwards and soars aloft, for in the world it finds nothing on which it can stand, nor ought it to cleave to created things, but to rest on God alone.
As the cable also by which the anchor is suspended joins the vessel with the earth through a long and dark intermediate space, so the truth of God is a bond to connect us with himself, so that no distance of place and no darkness can prevent us from cleaving to Him. Thus when united to God, though we must struggle with continual storms, we are yet beyond the peril of shipwreck. Hence he says, that this anchor is sure and steadfast, or safe and firm.
It may indeed be that by the violence of the waves the anchor may be plucked off, or the cable be broken, or the beaten ship be torn to pieces. This happens on the sea; but the power of God to sustain us is wholly different, and so also is the strength of hope and the firmness of His word.”
–John Calvin, Commentary on Hebrews 6:19, (Grand Rapids, Mi.: CCEL, 2005).