Deuteronomy 1:37 - 40

"Because of you the Lord became angry with me also and said, 'You shall not enter it, either. But your assistant Joshua son of Nun, will enter it. Encourage him, because he will lead Israel to inherit it. And the little ones that you said would be taken captive, your children who do not yet know good from bad - they will enter the land. I will give it to them and they will take possession of it. But as for you, turn around and set out toward the desert along the route to the Red Sea.'" NIV translation

Moses reminds them of his own disobedience and the fact that even he would not be entering the land. He reminds them of how their ancestors were told to go back towards the Red Sea. This was a return to the place where God had delivered them from the hand of the Egyptians.

Deuteronomy 1:41

"Then you replied, 'We have sinned against the Lord. We will go up and fight, as the Lord our God commanded us.' So every one of you put on his weapons, thinking it easy to go up into the hill country." NIV translation

Moses reminds the survivors of the fact that their ancestors had realized that they had sinned against God. Their lack of trust in Him to provide the victory was their sin. So, why did God still punish them and not let them enter the land? They were still thinking that they could take possession of the land through their own efforts. Like the Israelites, we do not have the ability to walk with Him under our own strength.