Christ has saved us from the power of darkness and placed all the benefits of that redemption package in our spirit man. It is however left to us to live out what God has given us through Christ Jesus by walking in faith and resisting all overtures of the devil to keep us trapped in a world of fear, doubt or spiritual stagnation.
It falls on us to enforce the victory Christ has won for us on the Cross by living according to the principles of God's word.
When doubt or fear comes knocking, we are to "resist the devil" and watch him flee from us. If we don't enforce our redemption rights by a strong walk in faith, our growth in the things of God might become stalled.
Grace to you.

Hebrews 12:1-3 NIV

Therefore, since we are surrounded by such a great cloud of witnesses, let us throw off everything that hinders and the sin that so easily entangles. And let us run with perseverance the race marked out for us, fixing our eyes on Jesus, the pioneer and perfecter of faith. For the joy set before him he endured the cross, scorning its shame, and sat down at the right hand of the throne of God. Consider him who endured such opposition from sinners, so that you will not grow weary and lose heart.