Faith comes from God because it is symbolized by the gold we are counselled to buy.
I counsel thee to buy of me gold tried in the fire, that thou mayest be rich; and white raiment that thou mayest be clothed, and that the shame of thy nakedness do not appear; and anoint thine eyes with eyesalve, that thou mayest see. (Rev 3:18, KJV)
The same symbolism is found in 1 Peter to describe faith as gold tried in fire:
That the trial of your faith, being much more precious than of gold that perisheth, though it be tried with fire, might be found unto praise and honour and glory at the appearing of Jesus Christ (1 Peter 1:7)
James also spoke of the same trying of our faith that brings about patience and makes us perfect (1:3-4)
In addition, we also see Paul mentioning that faith is a fruit of the Spirit:
But the fruit of the Spirit is love, joy, peace, suffering, gentleness, goodness, faith, meekness, temperance (Galatians 5:22-23)
Indeed, "every good gift and every perfect gift is from above" (James 1:17)
To summarize, faith is from God. Through trials and experiences we learn to exercise this faith and receive more faith. Therefore let us learn to "put on the whole armour of God" (Ephesians 6:11) and "above all, taking the shield of faith" (Ephesians 6:16).