Matthew 24:29-31

Be ready, in season and out of season, to give an account of your hope in Christ Jesus.

Jesus draws on various old testament traditions surrounding the Son of Man and the Day of the Lord to describe what it will be like at His Parousia. Faithlife Bible.

The Parousia is a theological concept that comes from the Greek word parousia meaning "coming" or "presence.". In the study of Bible prophecy, the term Parousia is used in reference to the Coming of Jesus Christ. In some cases, the Parousia is used in reference to the time when Jesus Christ comes to rapture His people…

Strong’s Concordance 3952 parousía (from parōn, "be present, arrive to enter into a situation") – properly, coming, especially the arrival of the owner who alone can deal with a situation (cf. LS). 3952 (parousía) is a "technical term with reference to the visit of a king or some other official, 'a royal visit' " (Souter) – "hence, in the NT, specifically of the Advent or Parousia of Christ" (A-S).

[3952 (parousía) is "used in the east as a technical expression for the royal visit of a king, or emperor. The word means literally 'the being beside,' thus, 'the personal presence' " (K. Wuest, 3, Bypaths, 33).]

The sign of the Son of Man probably refers to Christ Himself appearing in heaven. The tribes of the earth probably refers to Israel. The context here is the national repentance of Israel predicted in Zech. 12:10, 12. The Son of Man coming on the clouds will be a fulfillment of Dan. 7:13. NKJ Bible.

Matthew 24:29–31 (NKJV)

²⁹ “Immediately after the tribulation of those days the sun will be darkened, and the moon will not give its light; the stars will fall from heaven, and the powers of the heavens will be shaken. ³⁰ Then the sign of the Son of Man will appear in heaven, and then all the tribes of the earth will mourn, and they will see the Son of Man coming on the clouds of heaven with power and great glory. ³¹ And He will send His angels with a great sound of a trumpet, and they will gather together His elect from the four winds, from one end of heaven to the other.

Daniel 7:13 (NKJV)

¹³ “I was watching in the night visions,

And behold, One like the Son of Man,

Coming with the clouds of heaven!

He came to the Ancient of Days,

And they brought Him near before Him.

Zechariah 12:10 (NKJV)

¹⁰ “And I will pour on the house of David and on the inhabitants of Jerusalem the Spirit of grace and supplication; then they will look on Me whom they pierced. Yes, they will mourn for Him as one mourns for his only son, and grieve for Him as one grieves for a firstborn.