(a) Notice the Sin charged. It is merely negative--forgettest. There is no charge of positive hostility or of any overt act. This forgetfulness is most natural and easy to be fallen into. The constant pressure of the world. It indicates alienation of heart from God.
It is most common among us, far more so than active infidelity, far more so than gross sin, far more so than conscious hostility.
(b) The implied Criminality of it. He is the Rock of thy strength' and the God of thy salvation.' Rock is the grand Old Testament name of God, expressing in a pregnant metaphor both what He is in Himself and what in relation to those who trust Him. It speaks of stability, elevation, massiveness, and of defence and security. The parallel title sets Him forth as the Giver of salvation; and both names set in clear light the sinful ingratitude of forgetting God, and force home the question: Do ye thus requite the Lord, oh foolish people and unwise?'
(c) The implied Absurdity of it. What a contrast between the safe munitions of rocks' and the unsheltered security of these Damascene gardens? What fools to leave the heights and come down into the plain! Think of the contrast between the sufficiency of God and the emptiness of the substitutes. Forgetfulness of Him and preference of creatures cannot be put into language which does not convict it of absurdity.
