The Glory of YHWH (Psalms 24:1-2).
‘YHWH's is the earth and its fullness,
The world, and those who dwell in it.
For HE has founded it upon the seas,
And established it upon the floods.'
Note the continual parallelisms throughout the Psalm where the second statement repeats the idea of the first in a different way, typical of Hebrew poetry.
The initial verses make clear that YHWH, the One who is to seek entry into Jerusalem, is the Creator of the whole earth, Who therefore possesses it by right, together with everything that is in it, including the peoples (its fullness, and those who dwell in it). In the Hebrew YHWH in Psalms 24:1 is emphatic, ‘To YHWH belongs the earth', as is ‘He in Psalms 24:2. This vision of universality fits well with the ideas of worldwideness prevalent in David's day, as evidenced by Psalms 2, where the expectation was that one day his descendants would rule the nations with a rod of iron, nations who were meanwhile seen as helpless before him because YHWH was with him and he was YHWH's anointed. Compare also Exodus 19:5, ‘all the earth is Mine'; Deuteronomy 10:14, ‘to YHWH your God belongs the heaven, and the heaven of heavens, the earth and all that is within it'; Psalms 50:12, ‘every beast of the forest is Mine, and the cattle on a thousand hills'; Psalms 89:11, ‘the heavens are Yours, the earth also is Yours, the world and its fullness You have founded them'.
And this world is seen as ‘founded' (established securely) on the seas and the water sources that were under the ground, which regularly caused flooding (compare Psalms 33:7) but were controlled by YHWH, ‘you have set a bound that they may not pass, that they turn not again to cover the earth' (Psalms 104:9). We are not to see this as a pseudo-scientific explanation of the world, (Israel were not into scientific investigation), but as a description based on observation (just as we speak of the sun going down) and on the records in Genesis 1:6-9. There too the earth came up out of the waters, and was established above them. And whenever they went to the edge of the seas and looked in they could see the earth going down to its foundations in the seas. So that is how they described it.
But they did not see the earth as simply resting on the waters, for they described YHWH as the One Who ‘laid the foundation of the earth that it should not be moved for ever'. He ‘covered it with the deep as with an undergarment, the waters stood above the mountains', after which ‘at His rebuke they fled, at the voice of His thunder they hurried away, they went up by the mountains, they went down by the valleys, to the place which He had founded for them'. So the waters themselves were seen as established on solid earth, with dry land arising from them, and thus established upon them.
The major emphasis being brought out is that the earth on which men lived has been established by YHWH in the midst of the powerful and hostile seas which are, however, under YHWH's total control (Job 38:11), and over the waters that are under the ground as revealed, for example, by the springs that poured forth water in abundance (‘the water under the earth' - Exodus 20:4). The earth is firm and secure under His control, and all within it is His. All is thus submissive to His will, and man is kept safe within it, for floods will never again be allowed to destroy mankind (Genesis 9:11).
It is this Creator God Who will seek to enter Zion, the new city of David, and establish His dwelling in the holy mount.