Fiducia is the complete trust in something. It is a giving over to it, a complete believing and acceptance of something. This is the kind of faith that a Christian has in Christ. A Christian, therefore, has fiducia, that is, he has real faith and trust in Christ and not simply an acknowledgment that He lived on earth at one time. Ascentia is the mere mental acknowledgment of the existence of something. For example, James 2:19, "You believe that God is one. You do well; the demons also believe, and shudder." This verse shows the demons mental acknowledgment that God exists. But they do not trust in Him.
So, fiducia is the faithful trust Christians have in Christ to be their savior based on his death, burial, and resurrection.