Here we touch the humility of Therese. She speaks the truth. It only lasted a moment but it marked her entire life. It marks our soul in its deepest aspect, and it is indelible. One cannot change it.
Baptism is with a view to sanctifying grace.
It is so to have us live this direct contact with God, this participation in the very life of God. The character of Baptism is, therefore, only perfectly in act in this intimacy with the three divine persons. We must all ask the Holy Spirit to take hold of us in this fashion so that the mark of God upon our soul might be living. We all need the Holy Spirit to have us effectively live this participation in the life of God. This is what allows us to be faithful.