Psalms 135:8

8.He smote the first-born of Egypt He now reverts to those more special benefits, by which God had laid his Church and chosen people under obligation to his service. As it was the Lord’s believing people only whom he addressed, the chief point singled out as the subject of praise is God’s having adopted them, small as they were in numbers, from the mass of the human family. Again, there was the fact of his having set himself in opposition, for their sakes, to great kingdoms and mighty nations. The wonderful works done by God in Egypt and in Canaan were all just so many proofs of that fatherly love which he entertained for them as his chosen people. It is not strictly according to historic order to begin with mentioning the destruction of the first-born of Egypt; but this is instanced as a memorable illustration of the great regard God had for the safety of his people, which was such that he would not spare even so mighty and wealthy a nation. The scope of the passage is to show that God, in delivering his people, had abundantly testified his power and his mercy.