Did the first three plagues affect the Israelites in Goshen?
Yes. The first three plagues fell on Goshen, where Israel dwelt, as well as on the rest of Egypt. Only before the fourth plague did God sever or set apart Goshen, putting a division between His people and the other people.
Les teaches from Exodus chapter 8 that three plagues had already fallen and the fourth was about to fall. The first three plagues fell on Goshen, where Israel dwelt, as well as the rest of Egypt. Just before the fourth plague, God says in Exodus 8:22 that He will sever, separate, or set apart the land of Goshen in which His people dwell, so no swarms of flies would be there, to the end that thou mayest know that I am the Lord in the midst of the earth. Verse 23 repeats that He will put a division between my people and thy people. Les explains that this was the beginning of God totally mandating that the nation of Israel would be separated from all the other nations of the world, and that never left them.