Our system of doctrine is the Reformed faith, also called Calvinism (because John Calvin was the most important exponent of it during the Reformation). It pulls together the most significant doctrines taught in the Bible. These doctrines are set forth in the Westminster Confession of Faith and the Larger and Shorter Catechisms (with accompanying biblical references). Our system of doctrine is summarized in the following paragraphs:
The Bible
The Bible, having been inspired by God, is entirely trustworthy and without error. Therefore, we are to believe and obey its teachings. The Bible is the only source of special revelation for the church today.
God
The one true God is personal, yet beyond our comprehension. He is an invisible spirit, completely self-sufficient and unbounded by space or time, perfectly holy and just, and loving and merciful. In the unity of the Godhead there are three “persons”: the Father, the Son, and the Holy Spirit.
Creation and Providence
God created the heavens and the earth, and all they contain. He upholds and governs them in accordance with his eternal will. God is sovereign — in complete control — yet this does not diminish human responsibility.
The Fall and Redemption
Because of the sin of the first man, Adam, all mankind is corrupt by nature, dead in sin, and subject to the wrath of God. But God determined, by a covenant of grace, that sinners may receive forgiveness and eternal life through faith in Jesus Christ. Faith in Christ has always been the only way of salvation, in both Old Testament and New Testament times.
Jesus Christ
The Son of God took upon himself a human nature in the womb of the Virgin Mary, so that in her son Jesus the divine and human natures were united in one person. Jesus Christ lived a sinless life and died on a cross, bearing the sins of, and receiving God’s wrath for, all those who trust in him for salvation (his chosen ones). He rose from the dead and ascended into heaven, where he sits as Lord and rules over his kingdom (the church). He will return to judge the living and the dead, bringing his people (with glorious, resurrected bodies) into eternal life, and consigning the wicked to eternal punishment.
Salvation
Those whom God has predestined unto life are effectually drawn to Christ by the inner working of the Spirit as they hear the gospel. When they believe in Christ, God declares them righteous (justifies them), pardoning their sins and accepting them as righteous, not because of any righteousness of their own, but by imputing Christ’s merits to them. They are adopted as the children of God and indwelt by the Holy Spirit, who sanctifies them, enabling them increasingly to stop sinning and act righteously. They repent of their sins (both at their conversion and thereafter), produce good works as the fruit of their faith, and persevere to the end in communion with Christ, with assurance of their salvation.
Good Works and Christian Liberty
Believers strive to keep God’s moral law, which is summarized in the Ten Commandments, not to earn salvation, but because they love their Savior and want to obey him. God is the Lord of the conscience, so that men are not required to believe or do anything contrary to, or in addition to, the Word of God in matters of faith or worship.
The Church
Christ has established his church, and particular churches, to gather and perfect his people, by means of the ministry of the Word, the sacraments of baptism (which is to be administered to the children of believers, as well as believers) and the Lord’s Supper (in which the body and blood of Christ are spiritually present to the faith of believers), and the disciplining of members found delinquent in doctrine or life. Christians assemble on the Lord’s Day to worship God by praying, hearing the Word of God read and preached, singing psalms and hymns, and receiving the sacraments.
Adapted from What is the OPC? Basic Information to Acquaint You with the Orthodox Presbyterian Church