Not Because of Their Righteousness
In Deuteronomy 8 the warning is that they should not think that they will have conquered the land by their own power (Deuteronomy 8:17). Here is a warning for the thought that they got the land because they are better than the people in the land. Thus, as Christians, we should not think that God has given us spiritual blessings because we are better people than the people around us. As if we are more faithful and by our own merit have received those blessings.
Proofs of undeserved grace can be abused by the flesh by interpreting them as proof of its own justice and excellence. God shows that it is not a question of their righteousness, where the flesh is going to boast, but that they have entered the land because of the iniquity of the peoples. Israel is the rod in God’s hand to judge those peoples. Later Nebuchadnezzar will be the rod in God’s hand to remove Israel from the land (2 Chronicles 36:20-Ecclesiastes :).
Another aspect is the promise made to the fathers. That is what we see in the counsel of God. He has intended it and promised it to his fathers. The time of fulfilment of that promise has come.
God emphasizes the fact that there is no righteousness from us that underlies the blessing He has given us (cf. Ezekiel 36:32). That we may now possess blessings is only because Christ defeated our enemies on the cross: “When you were dead in your transgressions and the uncircumcision of your flesh, He made you alive together with Him, having forgiven us all our transgressions, having canceled out the certificate of debt consisting of decrees against us, which was hostile to us; and He has taken it out of the way, having nailed it to the cross. When He had disarmed the rulers and authorities, He made a public display of them, having triumphed over them through Him” (Colossians 2:13-Ezra :).