God fully intended for Israel to go to war and drive out the inhabitants of the Promised Land. God spoke this on the heels of giving the Ten Commandments and the terms of the covenant. These instructions, then, were spoken on the same occasion that God said, “Thou shalt not kill,” or to be more precise, “You shall not murder” (Exodus 20:13, NKJV).
At first glance at Exodus 23, it may appear that God would do all of the work: “I will cut them off”; “I will send My fear before you”; “I will cause confusion”; “I will send hornets”; “I will drive them out.” However, verse 31 also shows that God fully intended that Israel play a part: “I will deliver the inhabitants of the land into your hand, and you shall drive them out before you.” God is not directing the Israelites to escort a friendly populace gently out of their territory. The literal translation says that Israel should cast them out. Strength of arms would be required.
God did not promise to change their nature; these carnal people would fiercely resist and defend their land and their religion. Israel would have a fight on their hands—which God fully intended. He would be leading the fight against the inhabitants, which is why Israel would prevail. However, they were still responsible for cleansing the land of the Canaanites and other peoples.
Exodus 23:22 (“if you indeed obey His voice and do all that I speak”) shows that God's promises are conditional, but it is important to understand exactly what the conditions were. If Israel were obedient, God would be an enemy to their enemies. The implication is not that if Israel disobeyed they would have to go to war, but rather that, if Israel disobeyed, they would have a much harder time when they did go to war. But whether or not they were faithful, Israel was still responsible for removing the paganism and pagans from the land.
Verse 33 stipulates that the inhabitants shall not dwell in the land. This was not conditional on Israel's obedience—this was God's edict to His people so they would understand their responsibility. But if the Israelites were faithful, they would have God on their side, blessing their efforts. It is the same way with us: God gives us responsibilities, and if we are faithful to Him, He supplies the help we need to carry them out.
It was Israel's responsibility, then, to marshal an army to subjugate the people of the land. This is seen in Numbers 1, which takes place while Israel is still at Sinai about one year later. In between Exodus 23 and Numbers 1, the Israelites had transgressed with the Golden Calf (Exodus 32:1-35). Yet, even after their unfaithfulness, God still says twice that He would drive out the inhabitants (Exodus 33:2; 34:11).
Therefore, Israel's unfaithfulness did not nullify God's promise. Instead, Numbers 1 records God telling Moses to take a census and determine the number of men who were able to go to war. Fourteen times in that one chapter God repeats the instruction to number the men who were able to “go to war”—even though He had just recently confirmed His promise to fight on their behalf! God would be driving out the inhabitants, but He was also preparing the Israelites to engage the enemy. Clearly, it was still God's intent that Israel do its part within the fight.