Thou governest the pride of the sea. I have already observed that what the prophet has hitherto spoken generally concerning the power of God, is to be referred to the miracle of the deliverance of the Israelites from Egypt, which he now celebrates in express terms. According to the interpretation of some, God is said to still the impetuous waves of the sea, because he does not suffer it to break forth and overflow the whole world by a deluge. But I would read the 9th and 10th verses connectedly, and would understand the prophet as speaking of the Red Sea, which God divided to make a way for the chosen tribes to pass over. The Psalmist adds immediately after, that all the land of Egypt was overthrown as a wounded man By these words he magnifies the grace of God, which was displayed in the deliverance of the Church. He intended, there can be no doubt, to set before his own mind and the minds of others, the paternal love of God, to encourage both himself and others to have recourse to Him for succor, with the greater freedom and alacrity. And in affirming that God had broken in pieces his enemies with his mighty arm, he concludes from the past experience of the Church, that his mode of acting will be always similar, whenever in his infinite wisdom he sees it to be required.

Thou rulest the raging of the sea - The pride; the anger; the lifting up of the sea. That is, when the sea is raging and boisterous; when it seems as if everything would be swept away before it, thou hast absolute control over it. There is, perhaps, no more impressive exhibition of divine power than the control which God has over the raging waves of the ocean: and yet this was the power which Jesus exercised over the raging sea of Galilee - showing that he had the power of God. Mark 4:39-41.
When the waves thereof arise - In the lifting up of the waves; when they seem to raise themselves up in defiance.
Thou stillest them - At thy pleasure. They rise no higher than thou dost permit; at thy command they settle down into a calm. So in the troubles of life - the storms - the waves of affliction; they rise as high as God permits, and no higher; when he commands they subside, and leave the mind as calm as the smooth sea when not a breath of wind moves over its surface, or makes a ripple on its placid bosom.

Thou rulest the raging of the sea - Whoever has seen the sea in a storm, when its waves run what is called mountain high, must acknowledge that nothing but omnipotent power could rule its raging.
When the waves thereof arise, thou stillest them - Thou governest both its flux and reflux. Thou art the Author of storms and calms. There may be a reference here to the passage of the Red Sea, and the strong wind that agitated its waves at that time; as the next verse seems to indicate.

(i) Thou rulest the raging of the sea: when the waves thereof arise, thou stillest them.
(i) For as he delivered the Church by the Red sea, and by destroying Rahab, that is, the Egyptians, so will he deliver it, when the dangers are great.

Thou rulest the raging of the sea,.... The power, pride, and elation of it, when it swells, and foams, and rages, and becomes boisterous, and threatens vessels upon it with utter ruin and destruction; but the Lord, who has it under his dominion and government, restrains it; he has made and can manage it, and he only: his power over it is seen in assigning it its place, and ordering the waters of it to it when first made; in placing the sand for its boundary by a perpetual decree, which it cannot pass; by commanding the stormy wind to lift up its waves, and by making the storm a calm, and the waves thereof still; see Psalm 107:25, instances of this were at the universal deluge, and at the Red sea:
when the waves thereof arise, thou stillest them; when the sea lifts up its waves, and both lift up their voice, and make a noise, and roar, the Lord hushes them, and makes them still and quiet, as a parent its child when it cries, or a master his scholars, when they are noisy and tumultuous; so Christ rebuked the wind, and checked the raging sea, and made it calm, when the ship in which he was with his disciples was covered with its waves; and as this is mentioned here as an instance of the great power and strength of the Lord of hosts, so that was a proof and evidence of the true and proper divinity of our Lord Jesus Christ, Matthew 8:24, all this may be understood, in a mystical sense, of the sea of this world, and the wicked inhabitants of it, who are as the troubled sea, and cannot rest, casting up mire and dirt, reproaching and blaspheming God and man; and particularly of tyrannical princes and potentates, who are like the proud waters and raging waves of the sea; but the Lord on high is mightier than they, and can and does restrain their wrath and rage, so that his people have nothing to fear from them; see Psalm 124:3.

At the time of the poet the nation of the house of David was threatened with assault from violent foes; and this fact gives occasion for this picture of God's power in the kingdom of nature. He who rules the raging of the sea, also rules the raging of the sea of the peoples, Psalm 65:8. גּאוּת, a proud rising, here of the sea, like גּאוה in Psalm 46:4. Instead of בּשׂוע, Hitzig pleasantly enough reads בּשׁוא = בּשׁאו from שׁאה; but שׂוא is also possible so far as language is concerned, either as an infinitive = נשׂוא, Psalm 28:2; Isaiah 1:14 (instead of שׂאת), or as an infinitival noun, like שׂיא, loftiness, Job 20:6, with a likewise rejected Nun. The formation of the clause favours our taking it as a verb: when its waves rise, Thou stillest them. From the natural sea the poet comes to the sea of the peoples; and in the doings of God at the Red Sea a miraculous subjugation of both seas took place at one and the same time. It is clear from Psalm 74:13-17; Isaiah 51:9, that Egypt is to be understood by Rahab in this passage as in Psalm 87:4. The word signifies first of all impetuosity, violence, then a monster, like "the wild beast of the reed," Psalm 68:31, i.e., the leviathan or the dragon. דּכּאת is conjugated after the manner of the Lamed He verbs, as in Psalm 44:20. כּחלל is to be understood as describing the event or issue (vid., Psalm 18:43): so that in its fall the proudly defiant kingdom is like one fatally smitten. Thereupon in Psalm 89:12-15 again follows in the same co-ordination first the praise of God drawn from nature, then from history. Jahve's are the heavens and the earth. He is the Creator, and for that very reason the absolute owner, of both. The north and the right hand, i.e., the south, represent the earth in its entire compass from one region of the heavens to the other. Tabor on this side of the Jordan represents the west (cf. Hosea 5:1), and Hermon opposite the east of the Holy Land. Both exult by reason of the name of God; by their fresh, cheerful look they give the impression of joy at the glorious revelation of the divine creative might manifest in themselves. In Psalm 89:14 the praise again enters upon the province of history. "An arm with (עם) heroic strength," says the poet, inasmuch as he distinguishes between the attribute inherent in God and the medium of its manifestation in history. His throne has as its מכון, i.e., its immovable foundation (Proverbs 16:12; Proverbs 25:5), righteousness of action and right, by which all action is regulated, and which is unceasingly realized by means of the action. And mercy and truth wait upon Him. קדּם פּני is not; to go before any one (הלּך לפני, Ps 85:14), but anticipatingly to present one's self to any one, Psalm 88:14; Psalm 95:2; Micah 6:6. Mercy and truth, these two genii of sacred history (Psalm 43:3), stand before His face like waiting servants watching upon His nod.