A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
psa 13:1On title, see Introduction. The Psalmist, mourning God's absence and the triumph of his enemies, prays for relief before he is totally destroyed, and is encouraged to hope his trust will not be in vain. (Psa 13:1-6)
The forms of expression and figure here used are frequent (compare Psa 9:12, Psa 9:18; Psa 10:11-12).
How long . . . for ever--Shall it be for ever?
psa 13:2The counsels or devices of his heart afford no relief.
psa 13:3lighten mine eyes--dim with weakness, denoting approaching death (compare Sa1 14:27-29; Psa 6:7; Psa 38:10).
psa 13:4rejoice--literally, "shout as in triumph."
I am moved--cast down from a firm position (Psa 10:6).
psa 13:5Trust is followed by rejoicing in the deliverance which God effects, and, instead of his enemy, he can lift the song of triumph.