hebrews 11:1
"Now faith is the assurance of things hoped for, the conviction of things not seen"
by this we understand that Faith is itself a proof of spiritual quickening, and the rest of the chapter goes on to say that such Faith makes a man righteous before God
if we also embrace ephesians 2:8 which informs us that;
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God," … we understand that such saving faith is an alien virtue to natural man, and must first be instilled in him by a miraculous act of God - bringing a dead soul to Life by the power of the Holy Spirit, resurrecting that which was once dead in its Sin
(see verse 5)
now it's natural to have doubts
… but if we use the word 'natural' in all it's senses including 'fallen', 'perverse' and 'corrupted', then one's natural mind which is at enmity with God has need of being transformed by it's renewal* - which again, is a work of the Holy Spirit who imbues a man with Faith by the power of His word, for;
"Faith comes from hearing, and hearing through the word of Christ." - romans 10:17
so basically, if you want to have faith you need to go to the sole source of it: God's word – asking God the Holy Spirit to enliven it to you and thus make you faithful, so that you may be counted righteous in His sight
"Without Faith it is impossible to please God"
~
*ephesians 4:23
"…and to be renewed in the spirit of your minds,"
romans 12:2
"Do not be conformed to this world, but be transformed by the renewal of your mind, that by testing you may discern what is the will of God, what is good and acceptable and perfect."