Principle 3 is Baptism.
Q: Who should be baptized?
A: Having begun the Christian journey by turning my life over to God and trusting by faith in Christ, I am ready to be baptized in the name of the Father , Son, and Holy Spirit and to continue growing with Christ in the knowledge of what it means to be buried with Christ in a a watery grave and raised to live in a new way of life (Matt 28:19-20; Rom 6:3-4) (xiv)
The form of this is governed by a 'who' rather than a 'what'. The Interpreter points his correspondent to the plural of Hebrews 6:2 as an indicator of the physical (water), spiritual (Holy Spirit) and participative (in Christ's sufferings as a disciple) aspects of baptism understood biblically.(31) 'Baptism is a simple act that conceals a great mystery' (32). For the free church tradition, baptizing a professing believer commissions them 'participate in the mission of the triune God.'(35) The letter tells the story of William Carey's mission to India, before concluding with The Pilgrim's Progress. The Slough of Despond and the River of Death, which miry death-dealing obstacles bookend Christian's adventure, are read as baptismal imagery (37-38). Perhaps.
[Some take the bathing in the Interpreter's garden in Part II as more indicative of baptism, but Bunyan himself was famously undoctrinaire about the need for immersion before church membership. His marginal notes to that incident indicates Sanctification, not baptism, as the interpretative key, followed as this washing is by the 'Seal' indicating the Spirit (Ephesians 1:13, 4:30). Bunyan's marginal reference for the seal is to Exodus 13:9-10 where a sign is given as memorial to being brought out of Egypt which Bunyan attests as 'the contents and sum of the Passover', which arguably points to baptism via 1 Corinthians 10:1-2. Although there is no Scripture reference, Ephesians 5:26 may be in view tying washing to sanctification, as well as Titus 3:5.]
Back to the Interpreter's letter, and Freeman's catechesis: the 'who' matters rather than the 'what' and the 'how'. And although the answer of Principle 3 offers that the candidate is 'ready' there is an important sense in which that is a confession of faith rather than self-assured certainty. Who can know what the life of discipleship will bring? The Interpreter finishes his letter helping the reader see that whenever despair and trouble may strike, the good news is that in baptism the believer is 'already dead'! 'Remember your baptism and be thankful!' (38)