#1. The Word of God is the source of Faith and means by which to keep Faith strong because
Bible says in Romans 10:17 that "So then faith cometh by hearing, and hearing by the word of God."
#2. Faith can also come as a gift of the Holy Spirit, but this kind of faith is a special faith for a specific assignment, at a specific time.
1Cor. 12:8 For to one is given by the Spirit the word of wisdom; to another the word of knowledge by the same Spirit;
9 To another faith by the same Spirit; to another the gifts of healing by the same Spirit;
10 To another the working of miracles; to another prophecy; to another discerning of spirits; to another divers kinds of tongues; to another the interpretation of tongues:
#3. God gives every man a measure of Faith to begin their Christian Journey with according to Rom. 12:3 which says
"For I say, through the grace given unto me, to every man that is among you, not to think of himself more highly than he ought to think; but to think soberly, according as God hath dealt to every man the measure of faith."