מדרש אויף ישעיהו 26:6

“And so that you will relate in the ears of your son, and of your son's son, what I have wrought upon Egypt, and My signs that I have performed among them; and you will know that I am the Lord” (Exodus 10:2).
“And so that you will relate in the ears of your son” – the Holy One blessed be He revealed to Moses what plague He would bring upon them, and Moses wrote it in an allusion: “And so that you will relate in the ears of your son” – this is the plague of locusts, as it is stated: “Relate to your children about it” (Joel 1:3).⁵What is to be related appears in the following verse – locusts.
“Moses and Aaron came to Pharaoh, and said to him: So said the Lord, God of the Hebrews: How long will you refuse to humble yourself before Me? Let My people go, and they will serve Me. For if you refuse to let My people go, behold, tomorrow I will bring locusts into your border” (Exodus 10:3–4).
“Moses and Aaron came.… For if you refuse to let My people go…” – what is “behold, tomorrow I will bring locusts into your border”? But not in the borders of the descendants of Ḥam. In this regard it is stated: “For when Your judgments are in the earth, the inhabitants [of the world] learn righteousness” (Isaiah 26:9). Through the plague of locusts, they recognized until where the border of Egypt is.
“And your houses will be filled, and the houses of all your servants, and the houses of all the Egyptians; that neither your fathers nor your fathers' fathers have seen, from the day that they were on the earth until this day. He turned, and exited from Pharaoh” (Exodus 10:6).
“They will cover the face of the earth.… And your houses will be filled…He turned, and exited from Pharaoh” (Exodus 10:5–6) – what is this?⁶Why does the Torah state that “he turned, and exited”? That does not appear in the account of any other plague. It is because he saw that they were looking at each other and believing his words, and he left there so they would take counsel and repent.

[2] Another interpretation: Vision of Obadiah. It says, "God rebukes the wild beasts and so on" (Psalms 68:31). Rabbi Pinchas said about this, "David said to God, 'Master of the universe, You rebuke the wild beasts that come from the cane, and their king writes with a cane, seals and takes golden coins, as well as Ephah measures, governors, and scribes who take much gold from the people every day, the testimony of the mighty ones in the carts of the peoples, who eat the fat of the peoples and come with the strength of the mighty ones, the strength of Abraham and Isaac. They say of themselves, 'Esau the son of Isaac, and Isaac the son of Abraham, crouches in the dust for silver.' Even though they are angry with someone who sins, they accept his bribe and take money from him. Moreover, they scatter Israel from their Torah study and bring them into the evil inclination's desire, as it says, 'Foreign nations will crave your closeness' (Psalms 68:32). God said, 'I will uproot them from the world. But I and you and the Messiah will stand against them,' as it says, 'You will trample the poor, you will walk on their backs' (Isaiah 26:6). God's foot, as it were, is Edom, as it says, 'I will cast my shoe over Edom' (Psalms 60:9). The foot of the poor is the Messiah, as it says, 'He is poor and rides on a donkey' (Zechariah 9:9). The feet of the poor are Israel, as it says, 'How beautiful are your steps' (Song of Songs 7:2). Therefore, Obadiah was commanded to stand against all the kingdoms on behalf of Israel because they are difficult to overcome, as it says, 'The vision, rise up and let us wage war against her' (Obadiah 1:1)."

(Devarim 16:15) "Three times in the year": "times" signifies "festivals," as it is written (Isaiah 26:6) "the times" (i.e., festivals) of the poor," and (Song of Songs 7:3) "How beautiful are your (festival) times (of "steps" [to Jerusalem]) in sandals!"