Josh 24:19, “Joshua said to the people, ‘You are not able to serve the Lord. He is a holy God; he is a jealous God. He will not forgive your rebellion and your sins. 20 If you forsake the Lord and serve foreign gods, he will turn and bring disaster on you and make an end of you, after he has been good to you.’ 21 But the people said to Joshua, ‘No! We will serve the Lord.’"
I like their determination! Yet, when the previous generation met the Lord at Mount Sinai, they too had said, “All that the Lord has spoken we will do” (Exo 19:8). And just a few weeks later, they were worshiping a golden calf! So Joshua had to be stern so that they would grasp the importance of examining their hearts, and then rely upon grace rather than themselves: “You will not be able to serve the Lord, for he is a holy God.”
In one sense, it’s impossible for us to serve the Lord because we can’t match the standard or splendor of his holiness: He is a holy God! But that’s not what Joshua had in mind because the standard of our service is actually not God’s holiness, but the standard of relationship! So Joshua introduces the priority of relationship when he says: Yahweh is a jealous God! We won’t be able to serve the Lord if we’re not understanding the intimacy of this relationship! We’ve got to grasp the relationship part of this.
Joshua wasn’t telling them it would be impossible for them to serve God, but he was challenging them to understand what’s involved. Just as a husband and wife are faithful to their marriage vows and they jealously guard each other’s affection, so Israel’s walk with God would be determined by a sense of intimate connection and faithfulness. Their biggest need was to cleanse their hearts from all allegiance to other gods and pursue only the Lord who loves and jealously guards their relationship with him.