Exodus 5:3

And they said, The Name of the God of the Jehudaee is invoked by (or upon) us. We will go, then, to proceed three days into the desert, and offer the sacrifices of a festival before the Lord God, that death and slaughter befall us not.

LEST HE FALL UPON US WITH PESTILENCE. “Moses and Aaron wanted to say [to Pharaoh], ‘Lest He fall upon thee,’ but they showed respect to royalty.” Thus the language of Rashi. Rabbi Abraham ibn Ezra explained: “‘Lest He fall upon us; that is, including us Israelites, also you Pharaoh and all Egypt.’ Therefore when the Egyptians saw the slaying of the firstborn, they said, ‘We are all dead men,’ for the words of Moses now became clear to them when he said, Lest he fall upon us with pestilence, and therefore they drove them to go to sacrifice [to G-d].”
This explanation of Ibn Ezra is not correct, for Moses and Aaron were not commanded to say that Israel too would share in the punishment of pestilence or sword if they would not sacrifice [to G-d], and Moses and Aaron would by no means change anything in the mission of G-d.
By way of the Truth, [the mystic lore of the Cabala], this is the secret of the offerings, as they constitute a redemption from punishment, for before Him goeth the pestilence.. Ramban then proceeds to explain the end of the verse: or with the sword.
Or with the sword, this means the harsh [attribute of justice]. Moses said this because the Holy One, blessed be He, had commanded them, saying, And you shall say unto him: ‘The Eternal, the G-d of the Hebrews hath met with us. And now let us go … that we may sacrifice to the Eternal our G-d.’ and they said to Pharaoh, Thus saith the Eternal, the G-d of Israel: ‘Let My people go.’ Now Pharaoh was indeed a very wise man. He knew [of the existence of] G-d and acknowledged Him, as he — or his predecessor (above, 1:8). One Rabbi said that he was really a new king; the other said that it was the same king but he decreed new edicts, and comported himself as though he did not know him. — said to Joseph: Forasmuch as G-d had shown thee all this; a man in whom the spirit of G-d is., Verse 38. But Pharaoh did not know the Proper Name of G-d, [i.e., the Tetragrammaton], and accordingly, he answered, I know not the Eternal. Therefore they replied and said to him, as they were commanded, The G-d of the Hebrews hath met with us, mentioning to him only the G-d of the Hebrews, which is equivalent to E-il Sha-dai. They said, He hath met with us, relating to Pharaoh the exact language of the message they were commanded to bring him, and they explained to him that in this meeting which they would have [with G-d], it would be necessary for them to sacrifice before Him, lest the meeting be with pestilence, or with the sword. In a similar vein did Scripture set forth in connection with Balaam, as it is said, And G-d met Balaam, and he said unto Him: I have prepared the seven altars, and I have offered up a bullock and a ram on every altar.

'ויאמרו אלוקי העברים וגו, the Jewish people are not Egyptians but originated in Mesopotamia, across the river Euphrates, as their very name indicates, they are therefore bound by the rules of the G’d of that country, otherwise this G’d will smite them” [making them useless to you as slave-labour. Ed.]

אלוקי העברים, concerning your statement that you never heard of such a Being, He is the G’d of the Hebrews, the ones who cleave to the religious teachings of עבר, the grandson of Shem, son of Noach. Concerning your statement that you will not release the Israelites, you would do well to listen to His instructions פן יפגענו, as He would punish both us and you.

דרך שלשת ימים, “a distance of three days’ walk.” The plain meaning of the verse is that Moses requested to take the people to the desert in order there to offer sacrifices to their G–d. In the event that Pharaoh would ask: “why can you not offer these sacrifices right here?” Moses anticipated this question, and he added that unless we do it in the desert we will be subject to severe punishment by our G–d. (Compare Exodus 8,22 for further elaboration)