Presuppositions are suppositions that are made ahead of time. From the moment they’re made, they’re treated as if they are established facts. Yet, suppositions are only unknowns that are treated as if they were facts.
Jesus is real. We need not presuppose Him. We know Him. He reveals Himself and His Truth. All people can test this by asking Christ to be Savior and Lord of their lives, submitting themselves to His leading and teaching as the Holy Spirit begins to lead them into all truth. So no one has to take anyone else’s word for it. Whoever is willing to look at the evidence will find Christ.
“This means that no matter how convincing the evidence or good the logic, an unbeliever cannot come to the faith because his fallen nature will distort how he perceives the truth. The only thing that can ultimately change him is regeneration. To this end, the presuppositionalist seeks to change a person’s presuppositions to be in conformity with Biblical revelation.” ~ CARM page on presuppositional apologetics