Translated by Allan Menzies.
2. The 144,000 Sealed in the Apocalypse are Converts to Christ from the Gentile World.
These, then, who are sealed on their foreheads  from every tribe of the children of Israel, are a hundred and forty-four thousand in number; and these hundred and forty-four thousand are afterwards said in John to have the name of the Lamb and of His Father written on their foreheads, and to be virgins, not having defiled themselves with women. What else could the seal be which is on their foreheads but the name of the Lamb and the name of His Father? In both passages their foreheads are said to have the seal; in one the seal is spoken of, in the other it appears to contain the letters forming the name of the Lamb, and the name of His Father. Now these taken from the tribes are, as we showed before, the same persons as the virgins. But the number of believers is small who belong to Israel according to the flesh; one might venture to assert that they would not nearly make up the number of a hundred and forty-four thousand. It is clear, therefore, that the hundred and forty-four thousand who have not defiled themselves with women must be made up of those who have come to the divine word out of the Gentile world. In this way the truth of the statement may be upheld that the first fruits of each tribe are its virgins. For the passage goes on: "These were brought from among men to be a first fruits to God and to the Lamb; and in their mouth was found no guile, for they are without blemish." The statement about the hundred and forty-four thousand no doubt admits of mystical interpretation; but it is unnecessary at this point, and would divert us from our purpose, to compare with it those passages of the prophets in which the same lesson is taught regarding those who are called from among the Gentiles.
 Apoc. vii. 3, 4.
Reference address : https://www.ellopos.net/elpenor/greek-texts/fathers/origen/john-commentary.asp?pg=2