The Medrash continues with R. Judah's source for this from the scriptures below -
Why specifically with this plague, the plague of darkness did Moses stretch out his hand, wasn't it the case with all the other plagues that HaShem still tells Moses to stretch out his hand, yet in each of those plagues Moses still uses his staff, as its written -
So what is the difference here in the plague of darkness that Moses uses his hand to activate the plague as its written 'Moses stretched out his hand'
And in regards to the verse that says 'But all the children of Israel there was light in their homes' (verse below) the Chizkuni asks why is the location of the plague not effecting the Israelites not mentioned here like it is in all the other plagues, as in all the other plagues the Torah says in the land of Goshen (which is where the Israelites dwelled) - rather it specifies that the location the Israelites weren't effected was specifically in their house. The intention of the question here is why is the home of the Israelites mentioned as where the plague wasn't, when all the other plagues used the city of the Israelites to mention the location of the lack of plague.
And we will answer with the help of the Blessed HaShem, that here in truth, it was completely within the ability (hand) of The Holy One Blessed Be He to extend Pharaohs heart to simply and immediately send the Children of Israel out of his land, as we know that 'the hearts of Kings and Officers is in the hand of HaShem'.
Rather, the purpose of the exile and the redemption of Israel in Egypt was that all the inhabitants of the world became aware that there was a 'ruler over the palace' (A Lord that rules over the world). We know this as its written -
And every single plague had its own purpose of what it achieved, and the plague of darkness was to make known the divine providence of the Blessed HaShem in the lower realms (Earth), that He did, does, and will do in regards to all realities.
And behold, its written in the book of Kohelet by King Solomon
We have a wonder to ask about this verse. Do fools not have eyes on their faces like the other humans who happens to be wise would have, it's not possible that all fools can't physically see and walk in darkness? And furthermore, another question, when the verse says that a wise man has his eyes in his head, the verse should have said that the wise man walks in light, and the fool walks in darkness, to be congruent.
Its possible to explain by introducing the following teaching from the Talmud -
The teaching continues.. So the nations of the world immediately go out and prepare and build a Sukkah on their roofs, and then the Holy One Blessed be He shines down upon them the heat of the sun from the month of Tamuz, and then everyone quickly gets up and leaves their Sukkah due to the heat.
And later on in this Talmud it teaches -
The source in the Tanach from this teaching is from the following verse -
As well, lets look into this following teaching from the Talmud -
And behold, it is known that whoever has eye pains, or weak eyes, that person cannot tolerate strong light, rather the opposite, that light will even darken his ability to see. Even a person that has healthy and functioning eyes still cannot stair at such a strong light, specifically the light of the sun. The reason for this is that the power of our eyes are capped and limited.
And behold, when humanity discusses things of the intellect and gaining clarity, verbiage of light is always used (A lightbulb went off in my mind). And in matters of things that don't make sense to people or where there is a lack of clarity, verbiage of dark is always used (My mind is cloudy). Just like in a dark room one cannot see anything, so too, something that the mind cannot comprehend, that thing will be hidden from them and not able to be 'seen'.
And this is exact the intention of the following verse -
Since nothing is hidden from HaShem, there is always light with Him.
And if we look into the Holy writings of Israel, we can see the main difference between the nations of the world and the Children of Israel. Regarding Israel, they believe something that they cannot see or grasp, and because of that they are able to understand and perceive metaphysical realities (beyond the laws of nature), which matters of that category cannot be grasped by our rationale mind. This however is not the case with the nations of the world, in which case they only believe in what their eyes can see, and they don't believe that the Holy One Blessed be He created and oversees all that was created, and He alone does, did, and will act upon all of creation. And that He oversees the world personally, and for the nations, it's difficult for them to understand something well beyond what the rationale mind can comprehend.
And behold in the future to come, a great light, the hidden light, that was saved for the righteous will be released/revealed.
And as we already learned above that this light will be a great punishment to the wicked, and that the righteous will be healed by it, as the righteous at that time will be able to understand matters with the eyes of their mind what was not understandable until that point in time.
And regarding what we learned above about the time when the Holy One Blessed be He shines the sun on the nations of world (during Sukkot) from its peak heat in Tamuz. The explanation here is that this peak sun is a reference to the great light of the future that is destined to shine down on the world, and when that happens the nations of the world won't be able to deal with such a light, since they cannot comprehend what is above what is rationale and material, and then everyone will leave their Sukkah, which means that people will start to deny the Blessed HaShem and throw off the burden of His Kingship. Since they don't believe in anything that they cannot grasp and comprehend with their logic and understanding.
And this is also the explanation from what we said above regarding when HaShem removed the sun from its sheath, and the wicked get punished by it, and the righteous heal from it, as we had the verse from Malachi "But for you who revere My name a sun of victory shall rise to bring healing. You shall go forth and stamp like stall-fed calves."
And this is the intention of the question we had from what we learned above from King Solomon, that the wise man has eyes in his head, and not that the wise man walks in light, which was the opposite verbiage of how we describes the fool who walks in darkness. Based on what we said above that regarding someone who walks in light, a regular person can even be blinded by a strong physical light, so its not talking about physical light, this is why the verse says the wise man has eyes in his head, this is the eye of the mind! And this eye you can stare at a great light without being effected, since he is a wise man he is worthy to see with the eyes of his mind even matters that are metaphysical (above the laws of nature). And when it says that a fool walks in darkness, that his eyes of his mind get darkened from a great light.
And this settles our question. That even a fool, which we can translate as someone full of sin, as we see from the sages -
The fool mentioned above has eyes inside of his head just as the same as the wise man that has eyes in his head, however, he cannot use them to 'see' and understand matters above the logic of the mind.
And this is what the verse says over here, "And HaShem told to Moshe stretch your hand out over the heavens" - hand over here is a hint to the divine providence that was made known to the Egyptians that the Holy One Blessed be He oversees reality with personal oversight onto the whole of creation. And since wicked humans cannot fathom this, since they cannot believe in anything that their eyes cannot visualize and understand, so for them things become dark. And this was the purpose of the plague of darkness. Now with this we can explain the Medrash from above regarding where the darkness came from? Then Rabbi Judah says it came from an upper darkness, as it says in Pslams - "He made darkness His screen; dark thunderheads, dense clouds of the sky were His pavilion round about Him."
The explanation here is that the darkness that prevented the Egyptians from seeing was not a physical darkness at all! Rather it was spiritual light that caused the darkness since the Egyptians could not comprehend the power of HaShem who is above the laws of nature. Therefor HaShem specifically tells Moses to stretch his hand specifically and not his staff, to hint to the hand of HaShem which is divine providence from above that guides this whole world.
And this also is the explanation of the verse that for all the Children of Israel their was light in their homes, and it did not mention the land of Goshen, rather in their homes! The means to say that literally in the places where the Egyptians were standing right next to the Israelites there was a difference in that the Egyptians couldn't see anything and the Israelites were experiencing an incredible light. And based on what we said before that since Israel believes in things that they cannot see, they are able to perceive things above the understanding of the rationale mind, which is not the case regarding the nations of the world.