We can define Orthodoxy in no better way than in the words of the great 18th-century Russian Father, St. Tikhon of Zadonsk — a Saint whose fervent spirit is needed very much today by Orthodox Christians. We should read him more and practice what he teaches. St. Tikhon calls Orthodoxy “the true Christianity,” and he wrote a whole book under this title. But “true Christianity” does not mean just having the right opinions about Christianity — this is not enough to save one’s soul.
St. Tikhon in his book, in the chapter on “The Gospel and Faith,” says: “If someone should say that true faith is the correct holding and confession of correct dogmas, he would be telling the truth, for a believer absolutely needs the Orthodox holding and confession of dogmas. But this knowledge and confession by itself does not make a man a faithful and true Christian. The keeping and confession of Orthodox dogmas is always to be found in true faith in Christ, but the true faith of Christ is not always to be found in the confession of Orthodoxy… The knowledge of correct dogmas is in the mind, and it is often fruitless, arrogant, and proud… The true faith in Christ is in the heart, and it is fruitful, humble, patient, loving, merciful, compassionate, hungering and thirsting for righteousness; it withdraws from worldly lusts and clings to God alone, strives and seeks always for what is heavenly and eternal, struggles against every sin, and constantly seeks and begs help from God for this.” And he then quotes Blessed Augustine, who teaches: “The faith of a Christian is with love; faith without love is that of the devil” (“True Christianity,” ch. 287, p. 469). St. James in his Epistle tells us that “the demons also believe and tremble” (James 3:19).
St. Tikhon, therefore, gives us a start in understanding what Orthodoxy is: it is something first of all of the heart, not just the mind, something living and warm, not abstract and cold, some thing that is learned and practiced in life, not just in school. (Orthodoxy in America)