How does one enter in and begin the new life in Jesus? Simply put from scripture, through faith and baptism.
Faith at its heart is trust and obedience. We trust God’s word concerning Jesus, the good news, the power of salvation for all who believe. That Jesus indeed is the fulfillment of God’s promises through his Person and work on the cross (his death and resurrection) which opens the way into God’s kingdom. And faith is active in good works and a changed life. It is not merely intellectual assent. Faith is both repentant, turning from sin and from one’s own way to God. And it is submissive: committed to following the will of God in Jesus.
The New Testament does not know of any unbaptized believers except in the rare exception of the dying thief on the cross. Baptism into Christ in the words of scripture is to put on Christ, the initial rite for participation in Christ (Galatians 3; Colossians 2). It is sacramental in that sense, indeed participatory, or at least the sign of participation in Christ’s death and resurrection so that through baptism one’s old life of self and sin is gone, dead, and the new life in Christ of righteousness and devoted obedience to God is present. We in Jesus are to live out our baptism in the power of his resurrection life (Romans 6).
Through Christ and his death and resurrection, all things eventually are made new, judgment falling on the old that is not immersed into this. And all of us by faith enter into this, however halting and difficult it is for us. It isn’t easy to live this new life against the grain of the old life which still holds sway in the world. The beginning of this new life is found in the church and in all who are members of this church, members of Christ himself.
This is just the beginning, but it is the only place according to scripture where we start. In and through Jesus becoming one in him in his body, the church.