As you grow in faith, experientially, the way we feel it, it feels like we're getting worse, because the stronger your faith is, the weaker it feels. Strong faith never says, "I'm strong." St Paul writes, "When I am weak, then I am strong." Faith is at its strongest when it is at its weakest because that is when it is most dependent upon grace, upon Jesus Christ.Then he goes on to describe how we might feel on Christmas Eve when we're sentimental and surrounded by family and singing about Jesus being born. When we have a spiritual mountaintop experience and are happy, then we feel that our faith is strong. Contrast that to when we're in the emergency room with a loved one who may die, when we are heartbroken, when we are terrified and cannot pray anything but "Lord, have mercy."
Sanctification, a process of growing in faith, growing in good works, is a strange process in that there is a growth. But we don't feel it like a growth. We become more aware of our sins the holier we become.