The final strophe differs from the others in structure. It contains five verses instead of three, and the verses are (with the exception of the last) composed of three clauses each instead of two. Some commentators have supposed that vv. 16-19 are an addition to the original psalm, and think that they do not cohere well with the preceding. This view denies that there is any allusion in the closing verses to the passage of the Red Sea, and takes the whole as simply a description of a theophany, like that in Psalm xviii. But surely the writhing of the waters as if in pangs at the sight of God is such an allusion. Ver. 19, too, is best understood as referring to the path through the sea, whose waters returned and covered God's footprints from human eyes. Unless there is such a reference in vv. 16-19, the connection with the preceding and with ver. 20 is no doubt loose. But that is not so much a reason for denying the right of these verses to a place in the psalm as for recognising the reference. Why should a mere description of a theophany, which had nothing to do with the psalmist's theme, have been tacked on to it? No doubt, the thunders, lightnings, and storm so grandly described here are unmentioned in Exodus; and, quite possibly, may be simply poetic heightening of the scene, intended to suggest how majestic was the intervention which freed Israel. Some commentators, indeed, have claimed the picture as giving additional facts concerning the passage of the Red Sea. Dean Stanley, for example, has worked these points into his vivid description; but that carries literalism too far. The picture in the psalm is most striking. The continuous short clauses crash and flash like the thunders and lightnings. That energetic metaphor of the waters writhing as if panic-struck is more violent than Western taste approves, but its emotional vigour as a rendering of the fact is unmistakable. "Thine arrows went to and fro" is a very imperfect transcript of the Hebrew, which suggests the swift zigzag of the fierce flashes. In ver. 18 the last word offers some difficulty. It literally means _a wheel_, and is apparently best rendered as above, the thunder being poetically conceived of as the sound of the rolling wheels of God's chariot. There are several coincidences between vv. 16-19 of the psalm and Hab. iii. 10-15: namely, the expression "writhed in pain," applied in Habakkuk to the mountains; the word rendered "overflowing" (A.V.) or "tempest" (R.V.) in Hab. v. 10, cognate with the verb in ver. 17 of the psalm, and there rendered "poured out"; the designation of lightnings as God's arrows. Delitzsch strongly maintains the priority of the psalm; Hupfeld as strongly that of the prophet.