The Lord reigneth - See the notes at Psalms 93:1. This is the general fact to be dwelt upon; this is the foundation of joy and praise. The universe is not without a sovereign. It is not the abode of anarchy. It is not the production of chance. It is not subject to mere physical laws. It is not under the control of evil. It is under the government of a God: a wise, holy, intelligent, just, benevolent Being, who rules it well, and who presides over all its affairs. If there is anything for which we should rejoice, it is that there is One Mind, everlasting and most glorious, who presides over the universe, and conducts all things according to his own wise and eternal plan.
Let the earth rejoice - The earth itself; all parts of it; all that dwell upon it. As the earth everywhere derives whatever it has of fertility, beauty, grandeur, or stability, from God - as order, beauty, productiveness are diffused everywhere over it - as it has received so many proofs of the divine beneficence toward it, it has occasion for universal joy.
Let the multitude of isles be glad thereof - Margin, “Many, or great isles.” The Hebrew is many. So the Septuagint, the Latin Vulgate, the Chaldee, and the Syriac. The eye of the psalmist is evidently on the many islands which are scattered over the sea. Not merely the continents - the extended countries where nations dwell - have occasion for joy, but the beautiful islands - the spots of earth which have risen from the deep, and which are covered with fruits and flowers - these, too, have occasion to rejoice: to rejoice that God has raised them from the waters; that he keeps them from being overflowed or washed away; that he clothes them with beauty; that he makes them the abode of happy life; that he places them in the wastes of the ocean as he does the stars in the wastes of the sky, to beautify the universe. The idea in the verse is, that all the earth has cause to rejoice that Yahweh reigns.