Baptism consists of matter and form.
1. The Israelites' “baptism” into Moses
Here we see the express relationship of water Baptism to salvation and also the foundation of the required appeal and "heart" behind the Baptism. When we baptise in the name of the "Father Son and the Holy Ghost" we are making this appeal. Baptism requires not only water, but the words "Father Son and the Holy Ghost" and the intention of baptising. Catholics don't believe we are save by water alone. In Catholic theology all three of these things are necessary for a valid Baptism (water, words and intention). We think this passage outlines the necessity of water and of the appeal. When the eunuchs were traveling along the road and Philip evangelized them, one of them said
4. The baptism which John preached
41. Therefore, besides the theory of Limbo (which remains a possible theological opinion), there can be other ways to integrate and safeguard the principles of the faith grounded in Scripture: the creation of the human being in Christ and his vocation to communion with God; the universal salvific will of God; the transmission and the consequences of original sin; the necessity of grace in order to enter into the Kingdom of God and attain the vision of God; the uniqueness and universality of the saving mediation of Christ Jesus; and the necessity of Baptism for salvation. These other ways are not achieved by modifying the principles of the faith, or by elaborating hypothetical theories; rather, they seek an integration and coherent reconciliation of the principles of the faith under the guidance of the ecclesial magisterium, by giving more weight to God's universal salvific will and to solidarity in Christ (cf. 22) in order to account for the hope that infants dying without Baptism could enjoy eternal life in the beatific vision. In keeping with a methodological principle that what is less known must be investigated by way of what is better known, it appears that the point of departure for considering the destiny of these children should be the salvific will of God, the mediation of Christ and the gift of the Holy Spirit, and a consideration of the condition of children who receive Baptism and are saved through the action of the Church in the name of Christ. The destiny of unbaptised infants remains, however, a limit-case as regards theological inquiry: theologians should keep in mind the apophatic perspective of the Greek Fathers.