Exodus 12:23

For the Glory of the Lord will be manifested in striking the Mizraee, and He will see the blood upon the lintel and upon the too posts, and the Word of the Lord will spread His protection over the door, and the destroying angel will not be permitted to enter your houses to smite.

AND HE WILL NOT SUFFER THE DESTROYER TO COME IN UNTO YOUR HOUSES. This means the angel that brings destruction in the world at the time of a plague, similar to that which it says, And He said to the angel that destroyed the people: It is enough; now stay thy hand. It is not, however, a reference to the One Who brought the destruction in Egypt, since it was the Holy One, blessed be He, Who smote them.

לנגוף, to afflict them with the afflictions G’d will visit on the Egyptian people other than deadly plagues. Whenever the expression נגף is used it refers to afflictions that do not result in death. A well known example of this is found in Exodus 21,22 ונגפו אשה הרה ולא יהיה אסון, “and he pushes a pregnant woman without causing any death, etc.”

המשחית, the Egyptian people by one of G’d’s other attributes expressing His anger.

ולא יתן המשחית לבא, “and will not suffer the destroyer to come;” Rabbi Moshe finds this phrase difficult, as in the Haggadah shel Pessach, the author quoting verse 12 in our chapter, we are told expressly that G–d Himself carried out the plague of killing the firstborn, so that the angel of death was not involved in any way on that night. We must therefore understand the verses to mean that what is meant is that the angel of death by himself was not authorised to perform his duties on that night, only in conjunction with the Lord Himself. The Lord never acts alone, but is always accompanied by an angel or angels.