New Revised Standard Version
“But when you see the desolating sacrilege set up where it ought not to be (let the reader understand), then those in Judea must flee to the mountains;

Contemporary English Version
Someday you will see that "Horrible Thing" where it should not be. Everyone who reads this must try to understand! If you are living in Judea at that time, run to the mountains.

New American Bible
“When you see the desolating abomination standing where he should not (let the reader understand), then those in Judea must flee to the mountains,

Douay-Rheims Bible
And when you shall see the abomination of desolation, standing where it ought not (he that readeth let him understand): then let them that are in Judea flee unto the mountains.

And when you shall see the abomination of desolation, standing where it ought not (he that readeth let him understand): then let them that are in Judea flee unto the mountains.

the abomination.

Daniel 8:13 And I heard one of the saints speaking, and one saint said to another I know not to whom, that was speaking: How long shall be the vision, concerning the continual sacrifice, and the sin of the desolation that is made: and the sanctuary, and the strength be trodden under foot?

Daniel 9:27 And he shall confirm the covenant with many, in one week: and in the half of the week the victim and the sacrifice shall fail: and there shall be in the temple the abomination of desolation: and the desolation shall continue even to the consummation, and to the end.

Daniel 12:11 And from the time when the continual sacrifice shall be taken away, and the abomination unto desolation shall be set up, there shall be a thousand two hundred ninety days.

Matthew 24:15 When therefore you shall see the abomination of desolation, which was spoken of by Daniel the prophet, standing in the holy place: he that readeth let him understand.

*etc:

Luke 21:20-22 And when you shall see Jerusalem compassed about with an army, then know that the desolation thereof is at hand. . . .

where.

Lamentations 1:10 Jod. The enemy hath put out his hand to all her desirable things: for she hath seen the Gentiles enter into her sanctuary, of whom thou gavest commandment that they should not enter into thy church.

Ezekiel 44:9 Thus saith the Lord God: No stranger uncircumcised in heart, and uncircumcised in flesh, shall enter into my sanctuary, no stranger that is in the midst of the children of Israel.

let him.

Matthew 13:51 Have ye understood all these things? They say to him: Yes.

Acts 8:30,31 And Philip running thither, heard him reading the prophet Isaias. And he said: Thinkest thou that thou understandest what thou readest? . . .

1 Corinthians 14:7,8,20 Even things without life that give sound, whether pipe or harp, except they give a distinction of sounds, how shall it be known what is piped or harped? . . .

Revelation 1:3 Blessed is he that readeth and heareth the words of this prophecy: and keepeth those things which are written in it. For the time is at hand.

Revelation 13:18 Here is wisdom. He that hath understanding, let him count the number of the beast. For it is the number of a man: and the number of him is six hundred sixty-six.

then.

Luke 21:21-24 Then let those who are in Judea flee to the mountains: and those who are in the midst thereof depart out: and those who are in the countries not enter into it. . . .