The Apostles had a little handbook they followed in administering the seven Sacraments. We could call that handbook "The Teaching of the Apostles," but it was commonly referred to by the Greek word for "teaching" which was "The Didache."
Now, although writers through the first five centuries often referred to the Didache, every copy of it was lost, leaving us in doubt as to just how the Apostles administered the Sacraments.
Then a century ago a copy of the original Didache turned up in central Africa, and it told us some surprising things about how the Apostles administered Baptism and Confirmation. It said that they were only conferred on Holy Saturday.
It said that the Apostles saw the Baptism pool as representing the tomb of Jesus. They saw going down into the pool as an expression of our willingness to die to sin with Jesus.
St. Paul referred to this in verses 3to 5 in Chapter Six of his "Letter to the Romans."
"Are you unaware that we who were baptized into Christ Jesus were baptized into his death? We were indeed buried with him through baptism into death, so that just as Christ was raised from the dead by the glory of the Father we also might live in newness of life."
The Apostles believed that the baptized, by dying to sin, opened a place in their hearts for the Holy Spirit. The newly baptized, on their way to the Easter Eucharist, were met by the bishop who put the Oil of Chrism on their foreheads. The Chrism represented the Holy Spirt taking over that part of the new Christian's soul that was free from sin.