How do hymns transmit the substance of theology, support faith, and carry the gospel? Can hymns become a systematic theology for laypersons? How do hymns present the message of Christian truth, and interpret this gospel in different times? This article is based on the Hymnal Sèng- Si (1964 and 2009 editions) of the Presbyterian Church in Taiwan General Assembly, and offers research on the common hymns in the first 500 years of Christian history about how the church countered heresy, instituted the Nicene Creed, and made hymns its important apologetic tool. The essay presents seven models about the theological function of these hymns and discusses its practical implication for modern believers. The heresies modern Christians face are usually about distortion of doctrines. They share common features of denying Christ's divine nature, His birth from the Holy Spirit, and only accept the humanity of Jesus. They also deny the doctrine of the Trinity, exalt the founder of the organization as the supreme lord and promote doctrines of their own to attract followers. The author argues that it is when Christians are able to sing what they believe and believe what they sing in worship as well as in daily life that they will encounter the Lord, revive their spirituality, and bring revival to the church.