Testimony, conversion, and being born again are distinct but related principles. When we first come to suspect that there is a God, that He sent His Son to redeem mankind, the Holy Ghost begins to work within us. As Alma taught in the Book of Mormon, the Word “begins to swell within your breasts; and when you feel these swelling motions, ye will begin to say within yourselves–it must be that the…word is good, for it beginneth to enlarge my soul; yea, it enlighteneth my understanding.” This is testimony, the beginning of knowledge that the Word of God is good. It’s not a perfect knowledge by any stretch, but it is enough to act on.
Testimony will lead to a mighty change of heart provided the Word falls not on stoney soil and we permit the Holy Ghost to work within us. This mighty change of heart leads to a desire to shed the sins of our former lives and be born again. But as the name implies, rebirth is the first not final act. We are still spiritually young.
Conversion is the transformation process where our fallen selves are literally converted into new creatures in Christ. It is a process of becoming, of sanctification. This conversion from sinner to saint can only occur by the power of the Gift of the Holy Ghost. This is perhaps why the Lord, in His final hours, said to Peter, chief Apostle and witness to all of Christ’s ministry and miracles, “when thou art converted….” Peter and the Apostles had not yet received the Gift of the Holy Ghost or partaken of its transformative power, though they had felt His influence.
Through the process of testimony, new birth, and conversion our natures are changed into a state of glory, a process completed not begun at resurrection. Effort is required but powerless to purify. That cleansing comes through the merits of Christ, and Him alone.