"The Lord your God will drive out these nations before you little by little. You will not be able to destroy them all at once otherwise the wild animals will become too numerous for you" Deuteronomy 7:22

This is from the Henry and Richard Blackaby devotional Experiencing God day by day:

When God led his people into the promised land he did so step-by-step. If He had allowed them to annihilate their enemies at once the land would have been too difficult to manage. So He allowed some of the enemies to remain for a time in order to maintain the land and suppress the wildlife (Isn't He such a thoughtful and strategic God!? He cares deeply about the details.) In doing so, God taught his people to trust him step-by-step. He gave them only as much responsibility as they could handle at one time.

As God leads you and your Christian growth. He will allow challenges that match your character and relationship to Him. God will not totally change your character at once when you become a Christian. Rather, He will lead you through a process to become more like his son. He will keep working in an area in your life until it is controlled by the Holy Spirit.

You may eagerly desire maturity in every area of your character

but steady, gradual growth is more lasting.

God will not take shortcuts and his process of making you like Christ. He sees your life from eternity and will take as long as necessary to produce lasting spiritual growth in you.

Do not become inpatient while God is producing Christ likeness in you. Do not seek more responsibilities than those he has given you. Obey all that you know he has asked, and he will lead you at a pace that fits your present character and his purposes for you.