Throughout Christian history, the topic of how or when a believer in Jesus as the Risen Christ becomes a Christian has been debated, and the debate continues into the modern era. Honestly, the debate is based on the divide between the High Churches (those which are highly ritualized, like the Catholic and Orthodox Churches) and Low Churches (those that are highly informal, like the Baptists, Pentecostals, and the several "Free"/"Non-Denominational" Churches), and it is centered on whether simply holding the belief inside one's heart and acting as a Christian (which includes "confession" of Jesus as Lord and Savior), is enough to enter the community of believers, or whether the convert should be entered into the community only after receiving certain rituals, like Baptism and First Communion. And the major problem in resolving the issue is that both sides have scripture that supports their position.
The reason disagreements exist over how one becomes a Christian is because there are two problems that can create misunderstandings within the Christian community. There is some corruption ("sin") that we are born with, which influences how the story of Jesus Christ is heard, and many of the disagreements over how to become a Christian can be traced back to a disagreement on how to resolve the issue(s) created by the corruption. In addition to that, there is an evil spirit - Satan, or the Devil - who is constantly working to create confusion on how to be reconciled with God by creating non Christian religions around the world, and also by creating confusion on how Christians can be faithful to God and still participate in the cultures of the world around them.
Jesus Christ anticipated His Church having these kinds of problems, and made a provision to resolve the conflict(s).
The answer Jesus Christ gave is found at the end of the Gospel of Matthew, Jesus gives us two commandments beyond that of always act in love in all ways. He first tells his disciples to share the Communion meal, and then, in Mat 28, commissions them to "Go forth and baptize all nations in the name of the Father and the Son and the Holy Spirit." Along with many passages in the letter of James and elsewhere, this is the Scripture that the High Church uses to justify their position. The Low Church, by contrast, prefers to use the scriptures which suggest a more free-form version, such as those in Acts or Paul's letters, in which all that is necessary to be admitted into Christian community is right belief.
In any case, all Christian denominations do celebrate the sacrament of Baptism, the ritual for which always begins with a reading of Scripture, followed by a profession of faith (in the High Churches, this is done by a short responsory to the Apostle's Creed), the immersion or imposition of water, and finally the anointing of the newly baptized.