Day 171: The Necessity of Baptism

The Lord himself affirms that Baptism is necessary for salvation. He also commands his disciples to proclaim the Gospel to all nations and to baptize them. Baptism is necessary for salvation for those to whom the Gospel has been proclaimed and who have had the possibility of asking for this sacrament. The Church does not know of any means other than Baptism that assures entry into eternal beatitude; this is why she takes care not to neglect the mission she has received from the Lord to see that all who can be baptized are "reborn of water and the Spirit." God has bound salvation to the sacrament of Baptism, but he himself is not bound by his sacraments. CCC 1257

In today's reading, the Catechism discusses the necessity of Baptism. Christ Himself lays out this essential requirement (Jn 3:5) and it is attested elsewhere in Scripture by the Apostles (e.g. 1 Pet 3:21). The efficacy of baptism is also nearly universally taught by the Church Fathers. All must receive baptism in order to be saved, "but [God] is not bound by his sacraments". There are instances where baptism is not possible (e.g. Lk 23:39-43), which as the Catechism Compendium summarizes:

Since Christ died for the salvation of all, those can be saved without Baptism who die for the faith (Baptism of blood). Catechumens and all those who, even without knowing Christ and the Church, still (under the impulse of grace) sincerely seek God and strive to do his will can also be saved without Baptism (Baptism of desire). The Church in her liturgy entrusts children who die without Baptism to the mercy of God. (#262)

That this sacrament is so crucial for us, while the "ordinary ministers" are bishops or priests (deacons too in the Latin Church), emergencies allow even more:

In case of necessity, any person, even someone not baptized, can baptize, if he has the required intention. the intention required is to will to do what the Church does when she baptizes, and to apply the Trinitarian baptismal formula. the Church finds the reason for this possibility in the universal saving will of God and the necessity of Baptism for salvation. CCC 1256

I like this part from the Catechism Companion, Vol II:

Faith and Baptism are inherently linked. In the Gospel of Mark chapter 2, we read about the paralyzed man whose four friends brought him to Jesus. Scripture says, "When Jesus saw their faith, he said to the paralytic, 'Child, your sins are forgiven" (Mark 2:5). This is a case where the faith of someone else has spoken on behalf of the person who is forgiven. That is what we have when it comes to infant Baptism. (p. 106)