Lutherans believe the Bible is the first and only authoritative source for Christian faith and teaching. Like other Christians, they believe in the Trinity, that Jesus Christ was both God and man, that all humans are sinful since Adam and Eve (see original sin), and that humans are saved by Jesus' death on the cross. Lutherans believe that the central idea to all of their beliefs is that humans are saved by grace alone through faith alone because of Jesus Christ alone (see Justification (theology)). The main points of Lutheran theology were summed up in 1530 by Philip Melanchthon in the writing called The Augsburg Confession.