The apostle mentioned the words “born of God” or something similar to it several times in the epistle. He also mentioned it in the gospel account. Other words similar to it are “born from above” or “born again.” The doctrinal term is “regeneration.” Regeneration is about God giving us a new heart; it is God writing His laws in our hearts. John wrote that everyone who believes has been “born of God” (1 Jn 5:1). The apostle would reinforce that their message bears the testimony of water, blood, and Spirit. One would surmise that they also refer to the Father's testimony about Christ.