Tertullian’s Against Marcion refutes the division between an allegedly evil Creator and a separate, purely good god revealed by Christ. God’s eternity, unbegotten nature, creative power, justice, goodness, and judgment identify one unique divine Lord. Creation, conscience, the visible and invisible order, and even Marcionite practices involving water, oil, bread, and wine contradict rejection of the physical world. Marriage, established by the Creator, likewise cannot be treated as evil. The transition from the Law to the Gospel is a planned dispensation rather than a conflict between deities, and Paul’s teaching is consistent with the prophets and apostolic faith. Christ’s names, body, ministry, miracles, parables, judgments, prayer, teachings on marriage and wealth, passion, Eucharistic words, crucifixion, and resurrection fulfill Old Testament prophecy. The Transfiguration’s presence of Moses and Elijah, the call of the Gentiles, forgiveness, mercy, love of enemies, and care for the poor all reveal continuity with Israel’s God. Tertullian defends the real humanity and future resurrection of the flesh against Marcionite denial, arguing that Christ saves the body rather than discarding it. He also appeals to the antiquity and apostolic preservation of the four Gospels and accuses Marcion of selective textual alteration. Paul’s mission, the fullness of time, grace, the cross, moral discipline, spiritual gifts, and Christ’s final judgment belong to the Creator’s single plan of creation, redemption, and adoption. Unity of God, Christ, Scripture, prophecy, and salvation is the work’s central rebuttal to Marcionite dualism.