Faith is not a fruit in Galatians 5.  It is a reference to the character trait of faithfulness.  True faith is of the divine nature of God. How does faith come?  We can grow in faith by hearing and hearing the Word of God.  This is the only way God designed for faith to increase.  Faith is available to saved and unsaved people.  God is not a respector of persons.  The priniciple of faith is a spiritual law and works by the confession of words out of your mouth. We each receive the same measure of faith when we believe the report (Word of God) that we have heard.  There are no limits to how deep we can go when we believe the words that we speak.  When we believe the words we speak it shall come to pass because faith is automatically there.  Speaking the Word of God creates faith realities in your life.