Hebrews 10:22

Let us approach (God) with a true and sincere heart in unqualified assurance of faith, having had our hearts sprinkled clean from an evil conscience and our bodies washed pure with water. 

The Holy Spirit is our greatest ally by convicting our hearts. To keep our hearts, clear of an evil conscience we need to pay attention to the prompting of the Holy Spirit. Without a clear conscience our prayers and faith in God will be hindered. When we are diligent in protecting ourselves from the bad influences of the world our faith will not be weakened.