This is a depiction of the baptizing of an infant, who is being held by his mother. A priest with alb and stole and assisted by a young altar boy, is baptizing.
The sacrament of baptism is a Christian rite of initiation, marking entry into the Church, symbolizing cleansing from sin, and rebirth as a child of God through water and the Trinitarian formula (Father, Son, Holy Spirit). It’s considered the first sacrament, grafting believers into Christ, bestowing grace, and creating a permanent spiritual mark, performed by pouring or immersing in water, typically by a priest, deacon, or minister, for infants and adults alike.