For the king trusteth in the Lord. This is at once the ground and the result of God' s favour to him. God favours David because of his trust, and David trusts in God because of his favour. The result is that, through the mercy (or, loving-kindness, Revised Version) of the Most High he shall not be moved (comp.
Psalms 15:5; Psalms 112:6). The words appear to denote a conviction, as Professor Alexander says, that David "would never be shaken from his standing in God' s favour." This conviction we may well conceive him to have felt, and to have regarded as one that might fittingly be expressed by his subjects, in whose mouth he placed it.
But such a conviction is not always borne out by events, and David confesses elsewhere, that, at any rate, once in his life, after he had said, "I shall never be moved," God "hid away his face from him," and he "was troubled" (Psalms 30:6, Psalms 30:7).