The sea is his - Margin, as in Hebrew, “Whose the sea is.” That is, The sea belongs to him, with all which it contains.
And he made it - It is his, “because” he made it. The creation of anything gives the highest possible right over it.
And his hands formed the dry land - He has a claim, therefore, that it should be recognized as his, and that all who dwell upon it, and derive their support from it, should acknowledge him as its great Owner and Lord.