Albert Barnes on Revelation 21:25

And the gates of it shall not be shut at all by day. It shall be constantly open, allowing free ingress and egress to all who reside there. The language is derived from Isa 60:11. Isa 60:11. Applied to the future state of the blessed, it would seem to mean, that while this will be their permanent abode, yet that the dwellers there will not be prisoners. The universe will be open to them. They will be permitted to go forth and visit every world, and survey the works of God in all parts of his dominions.

For there shall be no night there. It shall be all day; all unclouded splendour. When, therefore, it is said that the gates should not be "shut by day," it means that they would never be shut. When it is said that there would be no night there, it is, undoubtedly, to be taken as meaning that there would be no literal darkness, and nothing of which night is the emblem: no calamity, no sorrow, no bereavement, no darkened windows on account of the loss of friends and kindred. Compare Barnes on "Re 21:4".

(e) "for there shall be no night" Zech 14:7