And God said, Let the waters under the heaven be gathered together unto one place, and let the dry land appear: and it was so.

Wesley's Notes

1:9-13 The third day's work is related in these verse s; the forming the sea and the dry land, and making the earth fruitful. Hitherto the power of the Creator had been employed about the upper part of the visible world; now he descends to this lower world, designed for the children of men, both for their habitation, and their maintenance. And here we have an account of the fitting of it for both; the building of their house, and the spreading of their table. Observe,
1. How the earth was prepared to be a habitation for man by the gathering of the waters together, and making the dry land appear. Thus, instead of that confusion which was, when earth and water were mixed in one great mass; now there is order, by such a separation as rendered them both useful.
(1.) The waters which covered the earth were ordered to retire, and to gather into one place, viz. those hollows which were fitted for their reception. The waters thus lodged in their proper place, he called Seas; for though they are many, in distant regions, yet either above ground or under ground, they have communication with each other, and so they are one, and the common receptacle of waters, into which all the rivers run.
(2.) The dry land was made to appear, and emerge out of the waters, and was called Earth. Observe,
2. How the earth was furnished for the support of man, Ge 1:11,12. Present provision was made, by the immediate products of the earth, which, in obedience to God's command, was no sooner made but it became fruitful. Provision was likewise made for time to come, by the perpetuating of the several species of vegetables, every one having its seed in itself after its kind, that during the continuance of man upon the earth, food might be fetched out of the earth, for his use and benefit.

Scofield Reference Notes

The third day: land and sea; plant life appears.

Jamieson-Fausset-Brown Bible Commentary

Ge 1:9-13. Third Day.

9. let the waters under the heaven be gathered together unto one place-The world was to be rendered a terraqueous globe, and this was effected by a volcanic convulsion on its surface, the upheaving of some parts, the sinking of others, and the formation of vast hollows, into which the waters impetuously rushed, as is graphically described (Ps 104:6-9) [Hitchcock]. Thus a large part of the earth was left "dry land," and thus were formed oceans, seas, lakes, and rivers which, though each having its own bed, or channel, are all connected with the sea (Job 38:10; Ec 1:7).

Matthew Henry's Concise Commentary

1:6-13 The earth was emptiness, but by a word spoken, it became full of God's riches, and his they are still. Though the use of them is allowed to man, they are from God, and to his service and honour they must be used. The earth, at his command, brings forth grass, herbs, and fruits. God must have the glory of all the benefit we receive from the produce of the earth. If we have, through grace, an interest in Him who is the Fountain, we may rejoice in him when the streams of temporal mercies are dried up.