The sign of the Son of man may be interpreted in at least two different ways: (1) The phrase may mean “the sign which is the Son of man,” thereby identifying the Son of man with the sign. In support of this interpretation are “the sign of the prophet Jonah” (12.39) and “the sign of Jonah” (16.4), where “the sign” is equated with Jonah himself. With regard to this interpretation, the Traduction œcuménique de la Bible (footnote) states “The sign is probably the Son of Man himself.”
(2) Other scholars argue that the sign and the Son of man are not to be identified. One commentator concedes that though this identification may fit with verse 3, it is practically impossible to accept on the basis of verse 30, where the Son of Man apparently appears after the sign is seen. Therefore a solution must be sought in another direction, and the clue is said to be the observation that Matthew alone mentions the sign and “the great trumpet” (verse 31). In Old Testament warfare trumpets and military standards (signs) are frequently mentioned together (Isa 18.3; Jer 4.21; 6.1; 51.27). Similarly, when Old Testament writers mention the day of the LORD, they attribute to it a standard of its own and a trumpet blast (Isa 27.13). And among the Jews who settled in Qumran, both trumpets and standards played a significant role. Following this line of argument, one may then conclude that the coming of the Son of Man to establish God’s Kingdom will be signaled by the raising of his standard and by the blast of a great trumpet.
Most translators will follow this second interpretation of the sign of the Son of man but will not make the sign explicit. Examples are “then people will see in the sky the thing which shows that the Son of Man is coming” and “then there will appear in the sky the thing that will make people know the Son of Man is coming.”
Translators should continue to render Son of man as in 8.20.
In heaven will be misunderstood by many readers as the place of God’s abode; “in the sky” (Good News Translation) signifies the region where the sun, moon, and stars are located, and clarifies what is meant by the phrase.
All the tribes of the earth will mourn derives from Zechariah 12.10-14, where tribes is used of the Jewish people. But for Matthew the quotation is enlarged to mean “All the peoples of the world” (New English Bible).
Mourn translates a verb which in the active form means “cut” or “cut off” (as in 21.8); when used in the middle voice it means “beat” (one’s breast as an act of mourning), the meaning it has here and in 11.17. New Jerusalem Bible (“beat their breasts”) and New American Bible (“will strike their breasts”) both focus upon the action itself without interpreting its significance. Most translations do it the other way around; they translate as “mourn” or “lament” without reference to the act of beating one’s breast. Bibel im heutigen Deutsch, 1st edition renders “will cry out in fear,” which is probably the best way to render it. Matthew is obviously describing the response of people who have not looked with anticipation for the coming of the Son of Man.
On the clouds of heaven differs from both “in clouds” (Mark 13.26) and “in a cloud” (Luke 21.27).
With power and great glory (so Luke 21.27) also differs from Mark (“with great power and glory” [13.26]). To come with power does not refer to the speed of his approach or the manner of coming, but rather to the fact that he will be seen to have great power as he comes. Glory in this context can mean radiance or splendor, but it is more likely that it refers to majesty. In either case, glory is something associated with God. Thus with power and great glory can be rendered by a short sentence: “He will have power and the great majesty of God” or “As he comes, people will see his power and the great splendor he has from God.”
Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .