Faith (4102) (pistis) in this context describes the Christian's personal confidence in God, Christ, His Word and His promises. Christians will be enabled to stand fearlessly firm against the roaring lion only if they lean wholly (which is what faith does) on Jesus' name, standing on the promises of God.
In Acts we read that the churches were being (passive voice = church acted upon by outside force, the Spirit of the Living God) strengthened (stereoo - verb form of stereos
over and over the church was being made firm and solidified like muscles) in the faith, and were increasing in number daily. (Acts 16:5)