To answer the question, Is Baptism necessary for salvation, we need to look to the Scriptures for direction. In John's Gospel, Jesus told Nicodemus: "I solemnly assure you, no one can enter into God’s kingdom without being begotten of water and Spirit." In Mark’s Gospel, Jesus tells the Apostles: "Go into the whole world and proclaim the good news to all creation. The man who believes in it and accepts baptism will be saved; the man who refuses to believe in it will be condemned."
Yes, according to God's plan, Baptism is the norm for salvation. However, we believe that God has not limited salvation to only those who are baptized in water. We read in I Timothy 2:4 that God "wills all men to be saved and come to know the truth." Given this fact of Revelation, the Church believes and teaches that God provides everyone many opportunities to be saved. If a person is not saved it is the choice of the individual person to reject the gift of salvation. The Church professes that all salvation comes through the Death and Resurrection of Jesus. As St. Paul states in Ephesians 2:8: "It is owing tohis favor that salvation is yours through faith. This is not your own doing, it is God's gift."
Accepting these truths, we ask the question: Does Baptism have to be by water? What about people who never had the opportunity of water Baptism through no fault of their own? Because God wills all men to be saved, the Church teaches that there are three forms of Baptism: by water, by fire and by desire. The first, by water, is clear enough. This is the ordinary way that most of us experience the gift of God's loving life for the first time and the way that we enter into the process of salvation. The second, by fire, affects those who may have been preparing for Baptism by water, but were martyred because they professed faith in Jesus Christ. This happened frequently in the early years of the Church. It may be happening today in areas where Christians are being persecuted.
The third, by desire, is more common than we think. Take, for instance, all the men and women before Christ's Death and Resurrection who were faithful to God. Jesus saved them. Their desire to follow God and do what He wanted them to do opened them to that gift of salvation. Or take the example of someone who, through no fault of his or her own, has never heard of Jesus and Baptism, but believes in God and lives according to their conscience in relationship with God. If that person is saved, it is because of Jesus Christ; and the desire of that person to be pleasing to God is the response to the call of God. Baptism by desire and Baptism by fire reflect the mysterious fulfillment of God's plan that everyone be given an opportunity for salvation.
With St. Paul, we too proclaim: "How deep are the riches and the wisdom and the knowledge of God! How inscrutable His judgements, how unsearchable His ways! For who has known the mind of the Lord? Or who has been His counselor? Who has given Him anything so as to deserve return? For from Him and through Him and for Him all things are. To Him be glory forever. Amen."For further detailed study please refer to "Catechism of the Catholic Church" pages 846, 1257-1261.