Tertullian was a great writer from about 190 to 200 after 200 AD he joined the Montanists heresy.

He made popular the Idea of three strikes and you are out theology. Although this is probably based on the fact that during the persecutions many went back to paganism. Later this would be interpreted that committing any kind of sin three times and you loose your salvation.

note: if the fathers believed in eternal security why did they just attach his three times idea instead of stating it is impossible anyway.

The teachings of Tertullian are as follows:

• Apology 5 - The Roman Senate rejected the petition to make Jesus officially recognized as a God.
• Apology 7 - We are accused of observing a holy rite in which we kill a little child and then eat it; in which, after the feast, we practice incest. 
• Apology 9 - In Gaul  children were sacrificed to Saturn and the old sacrificed to Mercury in the time of Tiberius. And the Romans crucified all the priests. Christians do not sacrifice young, old, or even destroy the fetus in the womb. Other pagan rites that Christians would never do are: cannibalism, blood letting to make a pact, eating raw flesh, blood sausage, human blood, incest, and adultery. The god Saturn was once a man, says historians.
• Apology 45 - Which is more perfect, to forbid adultery, or to restrain from even a single lustful look?
• Apology 46 - A Christian has grace-healed eyes and is mentally blind against the assaults of Adultery.
• Marcion 1.1 - "the fraud of a person who was then a brother, but became afterwards an apostate."
• Marcion 1.26 - God dislikes evil but will not punish it.
• Marcion 1.29 - Marcion forbids marriage and says it is evil. Married people can't be baptized unless they get a divorce. This is the opposite of the Nicolaitans. Christians do not prescribe celibacy as the rule, but only recommend it. Meats and drinks are not on this account to be condemned, because, when served up with too exquisite a daintiness, they conduce to gluttony; nor is raiment to be blamed, because, when too costly adorned, it becomes inflated with vanity and pride. There is a great difference between a cause and a fault, between a state and its excess. 
• Marcion 2.1 - It is incorrect logic to try to prove something by tarring something else down.
• Marcion 2.23 - It is not the mark of a good God to condemn beforehand persons who have not yet deserved condemnation. Who is so faultless among men, that God could always have him in His choice, and never be able to reject him? Or who, on the other hand, is so void of any good work, that God could reject him for ever, and never be able to choose him?
• Marcion 3.25 - In the resurrection we shall then be changed in a moment into the substance of angels
• Marcion 4.29 - Marcionites must be celibate.
• Marcion 4.35 - "the kingdom of God is within you." means "in your hand, or within your power", if you hear, and do the commandment of God.
• Marcion 4.37 - Christ saves both body and soul. heretics say the body is not saved (resurrected).
• Valentinians 1.32 - After death the Valintinians go to the pleroma and are purged of their animal nature. After the purging (purgatory)  they will marry the angels, even though they have no physical bodies or animal nature.
• Praxeas 1.1 - The Praxean heresy is that Jesus is the Father incarnate. After the Bishop of Rome had acknowledged the prophetic gifts of Montanus, Prisca, and Maximilla. Praxeas taught his heresy in conjunction with Montanus ideas. This lead to the bishop of Rome recanting Montanus and praxean ideas. (Tertullian was a Montanist at this time.)
• Praxeas 1.2 - Lateness of date marks all heresies.
• Idolatry 1.16 - Ceremonies or Holidays for man made events not directly connected with an Idol are OK.
• Nations 1.12 - The Cross is not an Idol. 
• Nations 1.16 - Christians do not commit incest.
• Prescription against heretics 1.22 Peter was is called "the rock on which the church should be built," who also obtained "the keys of the kingdom of heaven," with the power of "loosing and binding in heaven and on earth.
• Shows - Christians should not go to plays if they contain murder, idolatry, adultery ect.
• Treatise of the Soul 1.9 - A sister that has ecstatic visions in his church (talks to angels and the Lord) says souls or ghosts that have appeared to her have complete human form "soft and transparent and of an ethereal color". 
• Treatise of the Soul 1.34 - Simon used the money he offered to buy the Holy Spirit with, to buy Helen.
• Treatise of the Soul 1.41 - Man's soul is depraved by original sin. Just as no soul is without sin, so neither is any soul without seeds of good. 
• Treatise of the Soul 1.45 - Thus in the very beginning sleep was inaugurated by ecstasy: "And God sent an ecstasy upon Adam, and he slept."
• Apparel of Women 1.2 - Jewelry invented by those angels who fell.
• Apparel of Women 2.5 - Makeup is unlawful
• Apparel of Women 2.6 - Dying the hair is disgraceful
• Apparel of women 2.7 - God bids you to be veiled so you don't have to fix up your hair.
• Apparel of Women 2.8 - Men too should not dye hair and worry about appearance.
• Apparel of Women 2.11 - Christian women should dress simpler than gentile women to show modesty and holiness.
• On the Veiling of Virgins 1 - The vicar of the lord is the holy spirit.
• On the Veiling of Virgins 8 - To his day Corinthians still veil their virgins. (for safety)
• On the Veiling of Virgins 9 - It is not permitted to a woman to speak in the church;(34) but neither (is it permitted her) to teach, nor to baptize, nor to offer, nor to claim to herself a lot in any manly function, not to say (in any) sacerdotal office. 
• On Repentance 2 - Repentance is a divine thing, originated by god. 
• On Repentance 5 - Sin Never to Be Returned to After Repentance
• On Repentance 6 - Baptism Not to Be Presumptuously Received, It Requires Preceding Repentance, Manifested by Amendment of Life. (sprinkled)
• On Repentance 7-12 - Some one may repent once or twice but not a third time.
• On Prayer to his wife 1.2 - Marriage is lawful but not polygamy.