From Walter Brueggemmann’s Message of the Psalms:

Second, the relation to God in these psalms is not at all cozy , comfortable, or congenial. There is an edge of resentment and resistance here that involves some jeopardy of the relationship. The speaker has some of the “cards , ” which will be played only after Yahweh’s lead. Yahweh will be freely praised, but only when there is specific reason for praise. This is daring theology , for it suggests that unless God delivers, God will not be distinctive (Ps. 35: 10) . Unless God gives [Hebrew], God will not be great (Ps. 35:27). There is the hint that God is motivated by the possibility of praise, to act as he might not otherwise.