The Pauline Epistles are the letters said to have been written by Paul the Apostle. They are generally recognised as the earliest surviving Christian documents.
A comparison of several commentaries (and what they say about other commentaries) suggests the following classification.
The ones whose authenticity has not been seriously questioned are
Those whose authenticity has been questioned by some are
Those whose authenticity is considered most doubtful are
In addition, the Epistle to the Hebrews is traditionally ascribed to him, though it does not carry his superscription as all the others do and even some of the Church fathers questioned the attribution.
With the exception of Ephesians and, to a lesser extent, Romans, the epistles are not systematic statements of doctrine, but were written for particular purposes to people in particular circumstances. They were intended to encourage, to strengthen faith, to foster community, to correct deviant tendencies, to resolve disputes, and to tackle new problems that had arisen, including the problem of the non-happening of the Second Coming.
Although much theology is based on what he wrote, Paul was not writing theology, and different epistles have different emphases. In Romans, the epistle on which Martin Luther based his doctrine of justification by faith, the emphasis is on the saving power of faith, but in an earlier epistle, 1 Corinthians he has said that of faith hope and love, love is the "greatest".
The theology centres on the crucifixion and resurrection of Jesus, events which are expressed in different ways, but always with the understanding that they put right, for those who accept them, the relationship between God and humanity. There is no passage in which Paul clearly identified Jesus with God. Clearly he did not consider Jesus to be like other human beings, but far greater, the Messiah in Jewish tradition, and he used the phrase "son of God". The Christian church remained divided on the question of whether Jesus was God in the fullest sense for several centuries after: the Arian "heresy" held that Jesus was θεος but not ό θεος, god but not God.
Jesus Christ, after his death and resurrection, is seen as the head of the church, Christians living and worshipping together. In the later epistles, the church is seen as Christ's body.
In Paul's thinking the action of Jesus in reconciling the world to God was inspired by love, and this love should be echoed by humans' love for God and for each other – the guiding ethical principle for the family, for the Christian community, and for society. Beyond this, Paul expected Christian behaviour to be governed by the spirit of God, and in the epistle to the Galations he listed the fruits or outcomes of life in the spirit: love, joy, peace, patience, kindness, goodness, fidelity, gentleness and self-control. Most of these may be described as virtues. They stand in contrast to the behaviour of those not so governed: fornication, indecency, debauchery, contentiousness, envy, selfish ambitions, and so on. Scholars generally consider that some of his other precepts, such as wives being subject to their husbands, and slaves needing to obey their master, simply reflect the values of his time. Many Christians, though, believe these to be divine revelation binding till the end of the world. Paul does not envisage any re-ordering of society apart from an emphasis on mutuality of obligation.
What Paul asserts and the guidance that he gives convey some information about the early church. It is clear that the eucharistic meal was a central practice of the cult. There were communal meals which generated disputes over what meat could be served, but it is not clear whether these were the same as the eucharistic meals. There were occasions when there were ecstatic utterances, and these could be disorderly at times. Some of the utterances were more or less unintelligible, and some people were considered to have a special gift for interpreting them. There could also be doubt over whether the utterances were inspired by the Holy Spirit or by other spirits (and Paul offers guidance on distinguishing them).
If the Pastoral epistles (1 & 2 Timothy and Titus) are considered genuine, they give information on the officers of the early church, but it is more likely that they are from a later date.