Over the years I've noticed how complacency is one of the biggest problems for the believer. Complacency will cause believers to be spectators instead of participants. The bible tells us that we're not justified by works, but that's referring to the works of the Law. However, the works produced by faith are necessary. Jesus made it clear that our actions show our belief.
“Everyone therefore who hears these words of mine, and does them, I will liken him to a wise man, who built his house on a rock. The rain came down, the floods came, and the winds blew, and beat on that house; and it didn’t fall, for it was founded on the rock. Everyone who hears these words of mine, and doesn’t do them will be like a foolish man, who built his house on the sand. The rain came down, the floods came, and the winds blew, and beat on that house; and it fell—and great was its fall.” - Matthew 7:24-27