Upvote:2
Hebrews tells us that,
“...faith is confidence in what we hope for and assurance about what we do not see.” (11:1 NIV)
As well as,
“...without faith it is impossible to please God, because anyone who comes to him must believe that he exists and that he rewards those who earnestly seek him.” (11:6 NIV)
Faith pertains to our belief in the existence of God by default. With the added parameters of the cross, our faith rests in the Fathers agreement with the Son in providing a sufficient atoning sacrifice in Jesus' death whereby God's wrath is fully appeased. Faith is believing that Jesus is a sufficient savior on a spiritual level; bringing us into a restored relationship with God and not just a historical martyr who died for what he believed in.
Paul states this clearly in his letter to the Romans,
“This righteousness is given through faith in Jesus Christ to all who believe... for all have sinned and fall short of the glory of God, and all are justified freely by his grace through the redemption that came by Christ Jesus. God presented Christ as a sacrifice of atonement, through the shedding of his blood—to be received by faith. He did this to demonstrate his righteousness, because in his forbearance he had left the sins committed beforehand unpunished— he did it to demonstrate his righteousness at the present time, so as to be just and the one who justifies those who have faith in Jesus.” (3:22-26 NIV)
It was lengthy, but I hope that helps. :)