In ver. 15 another pregnant expression occurs, which is best filled out as above, the reference being to cleaving the rock for the flow of water, with which is contrasted in _b_ the drying up of the Jordan. Thus the whole of the Exodus period is covered. It is noteworthy that the psalmist adduces only wonders wrought on waters, being possibly guided in his selection by the familiar poetic use of floods and seas as emblems of hostile power and unbridled insolence. From the wonders of history he passes to those of creation, and chiefly of that might by which times alternate and each constituent of the Kosmos has its appointed limits. Day and night, summer and winter, recur by God's continual operation. Is there to be no dawning for Israel's night of weeping, and no summer making glad the winter of its discontent? "Thou didst set all the bounds of the earth,"--wilt Thou not bid back this surging ocean which has transgressed its limits and filled the breadth of Thy land? All the lights in the sky, and chiefly the greatest of them, Thou didst establish,--surely Thou wilt end this eclipse in which Thy people grope. Thus the psalmist lifts himself to the height of confident though humble prayer, with which the psalm closes, recurring to the opening tones. Its centre is, as we have seen, a double remonstrance--"How long?" and "Why?" The encircling circumference is earnest supplication, of which the keynote is "Remember" (vv. 2 and 18). The gist of this closing prayer is the same appeal to God to defend His own honour, which we have found in the former verses. It is put in various forms here. Twice (vv. 18 and 22) God is besought to remember the reproach and contumely heaped on his name, and apparently warranted by His inaction. The claim of Israel for deliverance is based in ver. 19 upon its being "_Thy_ turtle dove," which therefore cannot be abandoned without sullying Thy fame. The psalmist spreads the "covenant" before God, as reminding Him of His obligations under it. He asks that such deeds may be done as will give occasion to the afflicted and needy to "praise Thy name," which is being besmirched by their calamities. Finally, in wonderfully bold words, he calls on God to take up what is, after all, "His own" quarrel, and, if the cry of the afflicted does not move Him, to listen to the loud voices of those who blaspheme Him all the day. Reverent earnestness of supplication sometimes sounds like irreverence; but, "when the heart's deeps boil in earnest," God understands the meaning of what sounds strange, and recognises the profound trust in His faithfulness and love which underlies bold words.