To say that baptism gives one new life in Christ is heresy. To teach that someone who has been baptized has been given new life by that act and is therefore a Christian even if there's no evidence that such a person has saving faith will result in churches filled with unregenerate members who have a false sense of security in regard to their eternity--a very serious matter indeed. Anyone who doubts that this is the teaching of the Roman Catholic Church should read the following, as reported by Catholic News Service, May 9, 2018:
VATICAN – The baptismal font is a tomb in which a person dies to sin, and it is a womb through which a person is born to new life in Christ, Pope Francis said.
"Just as our parents generated us to earthly life, the church has regenerated us to eternal life through baptism," the Pope said May 9 at his weekly general audience.
Continuing a series of audience talks about baptism, Pope Francis said that from the time a person is baptized, God's voice repeats what God said at Jesus' baptism, "You are my beloved son. You are my beloved daughter."
"God loves us so much," the Pope told the crowd in St. Peter's Square.
"Reborn as children of God, that is what we'll be forever," he said. "Baptism, in fact, is never repeated because it imposes an indelible spiritual seal. No sin can erase this mark, even if sin prevents baptism from bearing the fruits of salvation. This baptismal mark will never disappear."
Pope Francis said he could imagine someone objecting, "But, Father, if someone becomes a criminal -- one of those infamous ones who kills people, who commits injustices -- won't the mark be gone?"
"No," the Pope responded. Although a person has sinned and turned from God, "God never disowns his children. Do you understand? God never disowns his children."
Baptism is a sacrament that purifies, sanctifies and justifies people, giving them the grace to conform themselves to Christ, he said. "Here lies the Christian vocation: to live united to Christ in his holy church," sharing its mission.
Consecrated to Christ in baptism, the Pope said, Christians are called "to make themselves an offering pleasing to God, giving witness to him through a life of faith and charity, putting oneself at the service of others following the example of the Lord Jesus."