Revelation 7:15

Therefore are they before the throne of God
(See Gill on Revelation 7:9); not because of their great tribulations, but because they were brought through them, and out of them, by the grace and power of God; nor because of their robes, or conversation garments, but because those were washed and made white in the blood of the Lamb; or because of the blood of the Lamb, and their justification, pardon, and cleansing by it:

and serve him day and night in his temple;
not in any material temple, but in the new Jerusalem, the general assembly and church of the firstborn, the temple of the living God; for in this state there will be no material temple, or place of worship, but God and the Lamb will be the temple thereof, ( Revelation 21:22 ) ; nor will there be any night there, ( Revelation 22:5 ) ; wherefore this phrase, day and night, only denotes the constancy and uninterruption of their service, there being nothing to obstruct them in it, or break them off from it, as now; in allusion to the priests and Levites, who were, one or other of them, night or day in the service of the temple: and the service of these persons in the new Jerusalem state will not lie in attending on the word and ordinances, or in the ministration of them, as in the present state; but in praising God, singing Hallelujahs to him, adoring the perfections of his nature, and admiring his wonderful works of providence and grace, and ascribing the glory of salvation to him, and to the Lamb; and this their service will be the glorious liberty of the children of God. Hence the Ethiopic version renders it, "and they praise him day and night"; this will be the employment of the saints in the millennium state, and to all eternity:

and he that sitteth on the throne shall dwell among them;
or "tabernacle over them"; for the tabernacle of God shall be now among men, and he will dwell among the saints; they shall enjoy his presence, and have the most intimate communion with him; it will appear most manifest that he is their covenant God, and they are his covenant people; and he will be a tabernacle, not only of inhabitation, but of protection for them; and the name of this city, this new Jerusalem, will be "Jehovah Shammah", the Lord is there.