Baptism

Mark 16:16
16 Whoever believes and is baptized will be saved, but whoever does not believe will be condemned.

John 3:5
5 Jesus answered, “Very truly I tell you, no one can enter the kingdom of God unless they are born of water and the Spirit.

Matthew 28:18-20 (ESV)
And Jesus came and said to them, “All authority in heaven and on earth has been given to me. Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you. And behold, I am with you always, to the end of the age.”