Reflecting on the Lord’s promises to Israel during the Babylonian siege, Swiss Reformed theologian Heinrich Bullinger (1504-1575) extrapolates their Christological implications. Thus, the “one heart” and the “one way” of the Old Testament are understood as the unity of the Christian faith, founded upon the one, true gospel of Jesus Christ. As there is only one way to salvation, he argues, Christians must remain united, rejecting sectarianism and forces that would threaten the unity of the church.
One in God: Community, Life, Covenant
“I will give to them one heart and one way.” The unity of hearts is accomplished in the unity of faith in one God; sincere love also joins with this one thing. In the Acts of the Apostles we read, “the faithful had one heart . . . ” Therefore, for some time after the Babylonian captivity the Jews were content with the one law of God; but thereafter they began to listen to the Tannaim and they became confused. In turn, true Christians do not attend to any teachings. Indeed, they are content with the evangelical, prophetic, and apostolic doctrine, which is the only true way of salvation. Christians are not torn apart into sects and orders. Thus the monastic orders are sects foreign to Christianity. Some sects and other sects [like them] do battle with this single way. Christ is the only true way; he is the only door; the truest teaching of Christ is the path, rule, and guide of piety, life, and eternal salvation. Let all decrees, decretals, assemblies, and laws perish when they do battle against the only way of God.
Sermon on Jeremiah 32:39-40.
Jeremiah, Lamentations, ed. J. Jeffery Tyler, Reformation Commentary on Scripture, OT vol. 11, p. 319.