Or HaChaim on Exodus 23:27/אור החיים על שמות כ״ג:כ״ז

1 את אימתי אשלח לפניך, "I will send My terror before you, etc." Even though G'd had said in verse 23 that He would cut off the inhabitants of the land of Canaan, G'd tells the Israelites here that this would not happen immediately but that He would first terrorise the Canaanite population during the time required for the Israelites to increase in numbers sufficiently to take over the country without leaving large areas empty of human beings. G'd hinted here that the conquest of the land of Canaan would proceed gradually, something spelled out in greater detail in verse 29.