Rom 8:3 For what the law could not do in that it was weak through the flesh, God did by sending His own Son in the likeness of sinful flesh, on account of sin:
The Apostle makes it clear of the law’s inability to free us from the dominion of sin. Moses the deliverer represents the law that was to lead the Israelites to the promised land, however he never made it there or lead them there. In a moment of weakness, he became angry and disobeyed God because of those He was leading. Here is a picture of the strong law being weak through the flesh.
God did not reject Moses (law), perhaps His aim was to demonstrate that it was not the law (Moses) that was to bring them to the promised land but Joshua (Jehovah saves) a picture of Christ. It was not Moses but Joshua who led the Israelites to the promised land. Gal 3:22-24, “22 But the Scripture has confined all under sin, that the promise by faith in Jesus Christ might be given to those who believe. 23 But before faith came, we were kept under guard by the law, kept for the faith which would afterward be revealed. 24 So then, the law was our guardian until Christ came, in order that we might be justified by faith.“