Defence. — Properly, high tower, as so often. The metaphor is important here from the contrast with the tottering wall of next verse.
Shall not be greatly moved... — i.e. (as in Psalms 37:24), shall not be made to totter or fall.
Related Commentaries of Psalms 62:2
Psalms 62:2
2 He only is my rock and my salvation; he is my defence;a I shall not be greatly moved.