Tertullian's apologetic writings are above all the most famous. They manifest two key intentions: to refute the grave accusations that pagans directed against the new religion; and, more proactive and missionary, to proclaim the Gospel message in dialogue with the culture of the time.

His most famous work, Apologeticus, denounces the unjust behaviour of political authorities toward the Church; explains and defends the teachings and customs of Christians; spells out differences between the new religion and the main philosophical currents of the time; and manifests the triumph of the Spirit that counters its persecutors with the blood, suffering and patience of the martyrs: "Refined as it is", the African writes, "your cruelty serves no purpose. On the contrary, for our community, it is an invitation. We multiply every time one of us is mowed down. The blood of Christians is effective seed" (semen est sanguis christianorum!, Apologeticus, 50: 13).

Martyrdom, suffering for the truth, is in the end victorious and more efficient than the cruelty and violence of totalitarian regimes.

But Tertullian, as every good apologist, at the same time sensed the need to communicate the essence of Christianity positively. This is why he adopted the speculative method to illustrate the rational foundations of Christian dogma. He developed it in a systematic way, beginning with the description of "the God of the Christians": "He whom we adore", the Apologist wrote, "is the one, only God". And he continued, using antitheses and paradoxes characteristic of his language: "He is invisible, even if you see him, difficult to grasp, even if he is present through grace; inconceivable even if the human senses can perceive him, therefore, he is true and great!" (cf. ibid., 17: 1-2).

Furthermore, Tertullian takes an enormous step in the development of Trinitarian dogma. He has given us an appropriate way to express this great mystery in Latin by introducing the terms "one substance" and "three Persons". In a similar way, he also greatly developed the correct language to express the mystery of Christ, Son of God and true Man.

The Holy Spirit is also considered in the African's writings, demonstrating his personal and divine character.

[Pope Benedict, General Audience, 30 May 2007]