I looked, and lo: see comments on “behold,” 1.7; 4.1.

Mount Zion: this was the hill on which stood the Jebusite stronghold that was captured by King David’s forces (see 2 Sam 5.6-7). The name was later extended in meaning to refer to the hill (Mount Moriah) on which Solomon built the Temple; sometimes it was used to speak of the city of Jerusalem. Here it represents the seat of the Messianic kingdom on earth, not in heaven itself.

The Lamb: see 5.6. Another translation model for this first sentence is “Then I looked and saw the Lamb standing there on Mount Zion.”

A hundred and forty-four thousand: this is the same number reported in 7.4.

His name and his Father’s name written on their foreheads: this may correspond to the seal of God upon the foreheads of his servants in 7.3 and 9.4. The passive written may indicate an angel as the one who did the writing. In many languages this final part of the verse will be rendered in a similar way to the following: “One hundred and forty-four thousand people were standing with him. These are the ones on whose foreheads they (unknown agents) have written the names of the Lamb and his Father.”

Quoted with permission from Bratcher, Robert G. and Hatton, Howard A. A Handbook on The Revelation to John. (UBS Handbook Series). New York: UBS, 1993. For this and other handbooks for translators see here .