On October 31, 1517, Martin Luther nailed 95 Theses opposing the Catholic sale of indulgences to the door of the Wittenberg Church in Germany. This is largely considered the catalyst for the Protestant Reformation which challenged the authority of the Roman Catholic Church with the authority of the Bible. The Church claimed to be the standard for doctrinal orthodoxy; Luther, Calvin, Bucer, Knox and many others asserted Scripture is that standard, and the responsibility of each Christian is to study and understand it for himself.
Reformed Christians embrace all the orthodox doctrines, including the Trinity, the full humanity and full deity of Christ, the necessity and efficacy of the Atonement, the Second Coming of Christ, etc. More distinctly Reformed doctrines are represented by the "solas": sola scriptura, sola fide, sola gratia, solus Christus, and soli Deo gloria (meaning Scripture alone, faith alone, grace alone, Christ alone, and God's glory alone).
Sola Scriptura: Scripture is God's specific revelation to mankind. Inspired by God (2 Tim. 3:16), it is authoritative, infallible and inerrant. Christians must submit to the Bible before any other authority, whether political, religious or vocational. It does not need supplementation, and nothing is to be added or taken from it (Rev. 22:18-19); the canon is closed.
Sola Fide: Justification is by faith alone (Acts 13:39; Rom. 5:1). This is not anti-nomianism (absence of law): we are bound by the law of grace, not free to do what we want but enabled to serve and obey Christ (Eph. 2:10). The Ten Commandments of the Mosaic covenant are not void because they represent the true character of God. However, no human could ever obey the entire law; Christ fulfilled it for us in its entirety (Matt. 5:17), and imputes that perfect obedience to all who have faith in Him.
Sola Gratia: The faith we have in Christ is not our own. He grants us faith because we have none (Eph. 2:8). We are dead in sin (Col. 2:13), and it is Christ's grace that brings us to life and sustains us as living people in the land of the dead (Rom. 6:1). No one deserves or earns Christ's grace (Eph. 2:9); it is a sign of His glory and compassion.
Solus Christus: Christ is our salvation. He is the head of the Church, its founder, its cornerstone. Everything in the Bible, everything in the world points to Christ. He is the focus of history and the purpose for creation (Col. 1:15). He is our sole access to God the Father (John 6:44). At the end of time, every created thing will sing the beauty and praise and glory of Christ (Rom. 14:11). Not the Church, not the law, not theology or doctrine can come before the preeminence, authority and power of Christ.
Soli Deo Gloria: Everything (everything) pertains to God's glory. The Westminster Catechism states, "The chief end of man is to glorify God and enjoy Him forever." Only God is worthy of glory and worship (Ex. 20:3; Deut. 6:4-5). God's primary purpose in history is not to save mankind and punish evil, they are merely aspects of His plan to glorify Himself.
Some people picture all Reformed Christians as grumpy old men with huge whiskers and an inability to smile (except maybe when the preacher describes the torments of hell to terrify poor sinners). While some dour Calvinists have doubtless contributed to this unfavorable image, most of the Reformed Christians we know are quite pleasant. Our joy comes from the love of God and the care He takes of His people. We are at peace knowing that God directs history, and that there will be no surprise ending—Christ wins and takes Christians to heaven to live with Him forever. Reformed theology isn't a winter wasteland of determinism and gloom, it is a bright springtime of hope and joy in Jesus Christ.
The best-known aspect of Reformed theology is its soteriology (doctrine of salvation) as explained by John Calvin. This system has been popularized and outlined as the "five points of Calvinism" (or TULIP). Essentially, they teach that:
Man is dead in sin and cannot choose God.
Psalm 14; Rom. 5:12
God sovereignly chose which people to save.
Christ's death on the Cross completely atoned for the sins of the elect.
Rom. 5:8-10; Gal. 3:13; Matt. 1:21
The work of the Holy Spirit, not the work of men, regenerates and calls the elect to salvation.
Rom. 9:16; 1 Pet. 1:3; Gal. 6:15; 2 Cor. 5:17-18; Eph. 2:1-5
God's people are preserved by Him in faith and righteousness.
John 6:47, 10:28-29; Rom. 8:29-30; 1 Cor. 1:7-9
Because of the doctrine of election, many believe Reformed Christians deny the importance of evangelism. This simply isn't true. We believe strongly in the need for evangelism and the transformation of society. This is not limited to making converts (though that's important); it includes involvement in every aspect of human society to claim the world for Christ as He commanded us. Reformed theology is not simply intellectual; it is intensely practical for all of life.