All this was done in obedience to the Lord’s command to Moses, which Moses passed on to Joshua. In fact, the entire purpose of this verse is to underline the absolute obedience of Joshua in doing everything that Moses had commanded him to do.

The LORD had given his commands may be taken as a reference to an indefinite number of general commands. However, in context the reference is to the specific command to destroy the inhabitants of the land. The relation between the last part of verse 14 and the first part of verse 15 becomes clearer if translated:

• That is what the LORD had commanded his servant Moses to do. Moses had told Joshua what the LORD had commanded, and Joshua obeyed the LORD’s commands. Joshua did everything that the LORD had commanded Moses.

Or:

• … Joshua completely obeyed the LORD’s command. He did everything that Moses had told him to do.

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 .