Fight to believe the gospel

From the introduction of a wonderful book on discipleship, written by Jonathan K. Dodson, called Gospel Centered Discipleship:

As we give and receive the gospel, we don't linger in imperfection, unbelief, disobedience, and failure. The Bible repeatedly tells us to fight. We have to fight to believe the gospel. Otherwise, we will slide back into individualistic, indifferent, or professionalized discipleship. This fight is a fight of faith. It is a struggle to believe what the gospel truly promises over what sin deceitfully promises. We need to remind one another that Jesus has not called us to performance or indifference but to faith in him. We need relationships that are so shaped by the gospel that we will exhort and encourage one another to trust Jesus every single day. (Dodson, Jonathan K. Gospel-centered Discipleship. Wheaton, IL: Crossway, 2012. Print. 18)