Rev 5:11-14  "And I beheld, and I heard the voice of many angels round about the throne and the beasts and the elders: and the number of them was ten thousand times ten thousand, and thousands of thousands; 12 Saying with a loud voice, Worthy is the Lamb that was slain to receive power, and riches, and wisdom, and strength, and honour, and glory, and blessing. 13 And every creature which is in heaven, and on the earth, and under the earth, and such as are in the sea, and all that are in them, heard I saying, Blessing, and honour, and glory, and power, be unto him that sitteth upon the throne, and unto the Lamb for ever and ever. 14 And the four beasts said, Amen. And the four and twenty elders fell down and worshipped him that liveth for ever and ever." 

The theme of the above four verses is praise and worship towards God.  We read in John 4:23 "But the hour cometh, and now is, when the true worshippers shall worship the Father in spirit and in truth: for the Father seeketh such to worship him. 24 God is a Spirit: and they that worship him must worship him in spirit and in truth."  Many who attempt to worship today do so in vain: Mark 7:7 "Howbeit in vain do they worship me, teaching for doctrines the commandments of men."  True worship gives all the praise, honor, and glory to God.  Any praise unto man is contrary to the true worship of God which the psalmist affirmed in Ps. 115:1 "Not unto us, O LORD, not unto us, but unto thy name give glory, for thy mercy, and for thy truth's sake."  The kingdom of heaven is described by the Lord here in time as being a little flock: Lk. 12:32 "Fear not, little flock; for it is your Father's good pleasure to give you the kingdom."  Yet in the morning of the resurrection that kingdom will be delivered up and expanded to include all the redeemed family of God: 1 Cor. 15:24 "Then cometh the end, when he shall have delivered up the kingdom to God, even the Father; when he shall have put down all rule and all authority and power."  All of the elect in the delivered up kingdom shall praise and glorify the name of God for his power, and wisdom, and strength, and honour, and glory, and blessing.  That will include a great host of angels and a multitude that no man can number of every nation, and kindred, and people, and tongue.  This includes "every creature which is in heaven, and on the earth, and under the earth, and such as are in the sea, and all that are in them."  I do not believe this to be anything other than the elect redeemed children of God.  They are the creatures under consideration:

          1.  Mk. 16:15 "And he said unto them, Go ye into all the world, and preach the gospel to every creature."

          2.  2 Cor. 5:17 "Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new."

          3.  Gal. 6:15 "For in Christ Jesus neither circumcision availeth any thing, nor uncircumcision, but a new creature."

          4.  Eph. 2:10 "For we are his workmanship, created in Christ Jesus unto good works, which God hath before ordained that we should walk in them."

          5.  Eph. 4:24 "And that ye put on the new man, which after God is created in righteousness and true holiness."

          6.  Col. 3:10 "And have put on the new man, which is renewed in knowledge after the image of him that created him:"

          7.  James 1:18 "Of his own will begat he us with the word of truth, that we should be a kind of firstfruits of his creatures."