For it was of the LORD to harden their hearts (Josh. 11:20, ESV)
This chapter is a difficult chapter. God is bringing His judgment on those who have consistently rebelled against Him. They’ve remained in their rebellion because of the hardness of their hearts and the Lord actually used their rebellion to incite further rebellion in them. God had fixed their hearts That’s why His judgment is always just and righteous.
F.B. Meyer has written,
They might have been saved, as Rahab was. And when it is said that God hardened their hearts, we must understand that their hearts became hardened by sinning against their light, in accordance with that great principle which God has established, that if a man resists his convictions of right he becomes more inveterate in his sinful ways. God is thus said to do what is done by the working out of the laws of that moral universe which He has constituted. It is clear that the Canaanites knew that God was with Israel. Rahab said (Joshua 2:10-11). And the Gibeonites (Joshua 9:10). There is no doubt, then, that throughout the land there had gone forth the fame of God; and when the kings flung their hosts in battle against Israel it was as it has always been (Psalms 2:2).For good news came to us just as to them, but the message they heard did not benefit them, because they were not united by faith with those who listened (Hebrews 4:2, ESV).
Brothers and sisters, let us not remain in the hardness of our hearts before the Lord. Rather, when we hear of Him and witness His power (as we do everyday all day with great clarity through His creation and in His Word), let us humble our hearts in repentance and faith. Otherwise we will find, as they did, a furthering hardening and will be justly judged in the wrath of God without mercy (Josh. 11:20). But, if we heed His voice we will find only mercy from a merciful and faithful high priest who has become the One to satisfy the wrath of God in our place (Heb. 2:17)