Arise, O Lord, into thy rest - Into that which is appointed for its permanent place of repose, that it may no longer be removed from spot to spot. This is spoken of the ark, considered as the place where God, by an appropriate symbol, abode. That symbol - the Shechinah - rested on the cover of the ark. The same language was used by Solomon at the dedication of the temple: “Now, therefore, arise, O Lord God, into thy resting place, thou and the ark of thy strength,” 2 Chronicles 6:41.
Thou, and the ark of thy strength - The ark, the symbol of the divine power, as if the power of God resided there, or as if the Almighty had his abode there. Perhaps the language was derived from the fact that the ark, in the wars of the Hebrews against their foes, was a symbol of the divine presence and protection - that by which the divine power was put forth.