A believer can encounter and strive against sin in two ways.
1) Endeavor to ward it off with all his might, seeking his strength in the Word and in prayer or...
2) Turn at the very moment of temptation to the Lord Jesus in silent exercise of faith and say "Lord, I have no strength. You are my keeper."
This is the method of faith. "This is the victory that has overcome the world; our faith" (1 John 5:4) Jesus who in himself is the one thing needed, can maintain the work of his Spirit in us. When we exercise faith with out ceasing, the blessing will flow in us without ceasing.
Christ must be all to us every moment. It is of no avail to me that I have life on earth unless that life is renewed every moment by my breathing of fresh air. Similarly God must actually renew and strengthen the divine life in me every moment. He does this for me in my union with Christ...the Spirit is simply the fullness of Christ, the life of Christ, and the self communicating love of Christ surrounding us as the air surrounds the body.
Excerpt from Chapter 8 of "Experiencing the Holy Spirit" by Andrew Murray
Fight. Every. Day.