Albert Barnes on Revelation 14:1

And I looked. My attention was drawn to a new vision. The eye was turned away from the beast and his image to the heavenly world--the Mount Zion above.

And, lo, a Lamb. Rev 5:6.

Stood on the mount Sion. That is, in heaven. Heb 12:22. Zion, literally the southern hill in the city of Jerusalem, was a name also given to the whole city; and, as that was the seat of the Divine worship on earth, it became an emblem of heaven--the dwelling-place of God. The scene of the vision here is laid in heaven, for it is a vision of the ultimate triumph of the redeemed, designed to sustain the church in view of the trials that had already come upon it, and of those which were yet to come.

And with him an hundred forty and four thousand. These are evidently the same persons that were seen in the vision recorded in Rev 7:3-8, and the representation is made for the same purpose--to sustain the church in trial, with the certainty of its future glory. Rev 7:4.

Having his Father's name written in their foreheads. Showing that they were his. Rev 7:3; Rev 13:16. In Rev 7:3, it is merely said that they were "sealed in their foreheads" The passage here shows how they were sealed. They had the name of God so stamped or marked on their foreheads as to show that they belonged to him. Compare Barnes on "Re 7:3, seq.

(a) "a Lamb" Rev 5:12 (b) "one hundred and forty-four thousand" Rev 7:4 (c) "Father's name" Rev 3:12