“for Yahweh your God is with you.” This does not mean God would be physically with Joshua, but that He supports him; God’s spirit was upon Joshua (Num. 27:18; Deut. 34:9), and God was working in and through him (cp. Josh. 1:17; 3:7; God was “with” Jesus, Acts 10:38). Note that here God changes to speaking about Himself in 3rd person. That technique in conversation can sometimes add emphasis, and it likely did for Joshua.