Joshua’s answer (verses 19-20) is that they must recognize the seriousness of their promise. They probably will not be able to keep it, which means that they will be punished for their idolatry. But you may not be able to serve the LORD may be translated either “But do not think that it is easy to serve the LORD” or “Do not be so quick to say, ‘We will serve the LORD.’ ” One may also translate “It is not easy to serve the LORD.”

Joshua reminds the people of Israel that the Lord is holy and that he will tolerate no rivals (Revised Standard Version “is a jealous God”). The first adjective holy stresses his essential being, the quality which characterizes God and separates him from sinful humanity. He is a holy God may be translated, “No other god is like the LORD,” “No other god can compare with the LORD,” or “The LORD is different from all other gods.”

The second adjective “jealous” is well represented by Good News Translation, He will tolerate no rivals (see Exo 20.5; Deut 4.24; 5.9) It represents the unwillingness of the Lord to share with any other god the exclusive claim that he has on his people, and so it may be translated “he demands (or, requires) absolute obedience.”

Will not forgive your sins represents “will not forgive your transgressions or your sins” (Revised Standard Version), in which Good News Translation combines the two nouns “transgressions” and “sins.” Furthermore, as a comparison of Revised Standard Version and Good News Translation will reveal, Good News Translation places the clause at a place other than where it is found in the Hebrew text. This is done in Good News Translation so that He will tolerate no rivals may be joined with and if you leave him … of verse 20. However, it seems more probable that will not forgive your sins should be joined with either (a) He will tolerate no rivals or (b) with both He will tolerate no rivals and He is a holy God. In context, “will not forgive your sins” then means that God will not forgive the sin of unfaithfulness to him. Upon the assumption that this analysis of the text is correct, the following translation results: “The LORD is a holy God who demands absolute obedience. He will not forgive you if you are unfaithful to him.” Or “The LORD is different from all other gods. He demands that you worship only him. If you worship other gods, he will not forgive you.” Either of these proposed restructurings will also have the advantage of leading nicely into verse 20: “If you leave him to worship foreign gods….”

Quoted with permission from Bratcher, Robert G. and Newman, Barclay M. A Handbook on Joshua. (UBS Helps for Translators). New York: UBS, 1983. For this and other handbooks for translators see here .