On Psalm 24

(Ps 24:1) The earth is the LORD'S, and the fulness thereof; the world, and they that dwell therein.

(Ro 11:36) For of him, and through him, and to him, are all things: to whom be glory for ever. Amen.

The fact that "the earth is the LORD'S, and the fulness thereof" has been applied in the following context.

(1Co 10:25)^EMTV Eat everything being sold in the meat market, questioning nothing, for conscience' sake;
(1Co 10:26) for "The earth is the LORD's, and all its fullness."
(1Co 10:27) And if any of the unbelievers invites you to dinner, and you desire to go, eat whatever is set before you, questioning nothing, for conscience' sake.
(1Co 10:28) But if anyone says to you, "This was offered to idols," do not eat it for the sake of the one who told you, and for his conscience' sake; for "The earth is the LORD's, and all its fullness."

Whatever people may have dedicated to other gods remains in the possession of God, since everything belongs to him. One was to abstain from food offered to idols only for the sake of those who were not mature in the faith, or who were not believers. The food itself was as good as food not offered to idols.

(1Ti 4:4)^MKJV For every creation of God is good, and nothing to be refused if it is received with thanksgiving.
(1Ti 4:5) For it is sanctified through the Word of God and prayer.

(Ps 24:1) The earth is the LORD'S, and the fulness thereof; the world, and they that dwell therein.
(Ps 24:2) For he hath founded it upon the seas, and established it upon the floods.

The word translated "floods" means "streams, rivers". The word for "upon" means also "above". The words for "earth" and "seas" are defined in Ge 1:9-10.

(Ge 1:9) 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.
(Ge 1:10) And God called the dry land Earth; and the gathering together of the waters called he Seas: and God saw that it was good.

Ps 24:2 may also refer to deep underground waters.

(Ps 24:3) Who shall ascend into the hill of the LORD? or who shall stand in his holy place?
(Ps 24:4) He that hath clean hands, and a pure heart; who hath not lifted up his soul unto vanity, nor sworn deceitfully.
(Ps 24:5) He shall receive the blessing from the LORD, and righteousness from the God of his salvation.
(Ps 24:6) This is the generation of them that seek him, that seek thy face, O Jacob. Selah.

In Ps 24:3, the Hebrew word translated "hill" is the word normally used to denote mountains. We also read in the New Testament that " ... ye are come unto mount Sion, and unto the city of the living God, the heavenly Jerusalem ... " (Heb 12:22). In Heb 12:22, the Greek word translated "mount" is the word used to denote mountains.

(Ps 24:7) Lift up your heads, O ye gates; and be ye lift up, ye everlasting doors; and the King of glory shall come in.
(Ps 24:8) Who is this King of glory? The LORD strong and mighty, the LORD mighty in battle.
(Ps 24:9) Lift up your heads, O ye gates; even lift them up, ye everlasting doors; and the King of glory shall come in.
(Ps 24:10) Who is this King of glory? The LORD of hosts, he is the King of glory. Selah.

The passage above may remind us of the time when the Lord will return. However, this application to the return of the Lord might not fully explain Ps 24:7-10. Another possibility would be to associate Ps 24:7-10 with the new Jerusalem (Rev 21:2). This would explain why the doors are everlasting in Ps 24:7, 9. Still another interpretation is possible. In the Bible, heads of gates are only mentioned in Ps 24:7, 9. Speaking of heads of gates would be natural if gates represent people. By taking gates as a figurative description of people, Ps 24:7-10 urges people to allow the King to come in. Since people are everlasting, some living forever in hell and the others forever in heaven, the words "everlasting doors" would fit this interpretation.

(Rev 3:20)^MKJV Behold, I stand at the door and knock. If anyone hears My voice and opens the door, I will come in to him and will dine with him and he with Me.