The answer
The Holy Mysteries of Baptism and Chrismation are carried out by the grace of the Holy Spirit through the prayers of the priest and the faith of the catechumen to be baptized. During the ceremony, the priest prays asking the Lord to make the person worthy of the baptism. Thereafter it is up to the person to really accept this prayer and be ready in his heart.The priest asks the person getting baptized to stand facing the East towards the altar of the Lord and raise their/her right hand declaring their faith saying, "I accept You, O Christ, my God with all Your Holy Commandments all Your life-giving service and works."
If the person is just lip-reciting these words, they might deceive the priest and the congregation; but will not deceive the All-knowing, discerning Holy Spirit.
So this Baptism and this Chrismation are not effective unless the person truly believes. If later on the person believes they do not need to be re-baptized for all the rituals has been performed and it is the Holy Spirit that will confirm this person and make those mysteries effective in their life at the right time.
Answered by His Eminence Metropolitan Youssef (opens in a new tab)