They are at the service of charity which builds up the Church. Since it belongs to the supernatural order, grace escapes our experience and cannot be known except by faith. We cannot therefore rely on our feelings or our works to conclude that we are justified and saved. This final item in particular, raises an important point. You can't use feelings to determine the existence of any element of the spiritual world.
Feelings come and go.
This is normal, right, and necessary. That's why Love isn't a feeling, it's an act, and a commitment. So are faith, Providence and grace. Like faith, and Providence, grace is not detectable by any ordinary means. It is discerned or deduced from events in our lives, and though feelings fluctuate, it persists.