Confirmation was tied to baptism as well as the rite of communion in the early church. As time passed, baptism, the Eucharist and confirmation were disentangled and the ceremony of Confirmation because synonymous with spiritual growth. Baptism was the sacrament of the initial gift of the Spirit, while confirmation was the sacrament of the fullness of the Spirit. When in the Middle Ages it became the practice to confirm close to adolescence instead of infancy, theologians began to teach that confirmation was the sacrament of maturity. Those who received it were regarded as old enough and ready to live active, responsible Christian lives. Modern theology links baptism to confirmation; but the two ceremonies are complementary. Confirmation does not complete baptism in the sense that baptism left something incomplete. Rather, the two sacraments are united in the initiation process. The read about confirmation’s roots and its progression to modern practices, read this detailed piece by Loyola Press.