Knowledge is the sister of Good Deeds and the two have accompanyed Everyman to the point of death. Knowledge, which is the knowledge of the teachings of the Church, has been very helpful to Everyman during his life. She has taught him to confess to the priest and to repent of his sins. With Knowledge's help, Good Deeds, who was very weak, has grown much stronger.
However, although very helpful in life, Knowledge can't help after death when one meets one's Maker and faces final judgment. This is because it is not what you know that can help you in the afterlife, but what you did with the knowledge. What you did is your Good Deeds, and these you do carry with you into the afterlife. Therefore, only Good Deeds descends into the grave with Everyman.