So is the kingdom of God....First the blade, then the ear, after that the full corn in the ear. Mark 4:26-28.
It would be wonderful if it were true that from the first time we were brought to the place of giving up on ourselves and surrendering our will to Christ we had uninterrupted victory. But we must face reality. A growing Christian does not experience constant dependence upon God's power. When God plants a tree, He plants a seed. When He plants corn, first comes a blade, then the ear, and after that the full corn in the ear. So there's no need for discouragement when we realize that our obedience is not perfect all the time.
In the first place, God doesn't accept us because of our obedience. He accepts us when we come to Him, presenting the merits of Jesus in dying in our place. Our acceptance before Him, and the certainty of our salvation, is already settled, as we continue to accept what Jesus did for us at the cross. And second, God Himself allows for growth.
The only way to victory and obedience is to look to Jesus, and what He has done and wants to do in our lives. As we grow as Christians, our trust and our total dependence upon His power is going to be inconstant. At times we will remember that we cannot overcome Satan in our own strength. We won't even try. We will look to Jesus for victory, and He will give it to us. At other times we will think that we can manage things ourselves, and we will fall and fail and end up in defeat. But this is not reason for discouragement. God has provided power for us to obey, and also forgiveness and pardon for sin.
There is a statement that I think should be written in the flyleaf of every Bible: "There are those who have known the pardoning love of Christ and who really desire to be children of God, yet they realize that their character is imperfect, their life faulty, and they are ready to doubt whether their hearts have been renewed by the Holy Spirit. To such I would say, Do not draw back in despair. We shall often have to bow down and weep at the feet of Jesus because of our shortcomings and mistakes, but we are not to be discouraged. Even if we are overcome by the enemy, we are not cast off....As we come to distrust our own power, let us trust the power of our Redeemer."--Steps to Christ, p. 64.