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By preaching the Gospel. Also by living an exemplary life.
The very life of Jesus, the preaching of Jesus, the written works themselves.
He became far more courageous in preaching the Gospel, & knowledgable in what was God's Will.
I can not speak for Andrew but will venture a guess that the day he met Our Lord and was chosen by him to be an apostle - the first apostle - would be a good bet.
St. John the Apostle lived in various places throughout his life, including Jerusalem, Ephesus, and possibly Patmos. He was one of the twelve apostles chosen by Jesus and is known for writing the Gospel of John, three epistles, and the Book of Revelation in the Bible.
The gospel is first four books in the new testament of the bible by Matthew, Mark, Luke and John, all about the life of Jesus.
Most of the books of the New Testament were written by apostles or other disciples of Jesus Christ. Matthew the apostle wrote a gospel. John the apostle wrote a gospel, three epistles and Revelation. Peter the apostle wrote two epistles, although recent scholarship has indicated that "2 Peter" was written many decades after his death by a follower. James and Jude each wrote an epistle, but they are probably not the two apostles by those names but two others known as brothers of the Lord. Mark, a follower of Peter, wrote a gospel. Luke, a follower of Paul, wrote a gospel and the Acts of the Apostles. Paul, an apostle but not one of the twelve who followed Jesus Christ during his public life, wrote 13 epistles. The author of the Epistle to the Hebrews is unknown.
Saint Andrew was one of the 12 apostles of Jesus, known for his strong faith and martyrdom. He was chosen as a saint due to his dedication to spreading Christianity and his willingness to sacrifice his life for his beliefs. His importance in the early church and his example of selflessness and devotion led to his canonization as a saint.
The gospel of John
The Claretians honor Saint Anthony Mary Claret, their founder and patron saint. He was a Spanish Roman Catholic archbishop and missionary who dedicated his life to preaching the Gospel and serving the marginalized.
Many think Mark's Gospel was written very early, possibly before all the others.
The author of the Book of Mark in the Bible is traditionally believed to be John Mark, a companion of the apostle Peter. Mark's Gospel is the shortest of the four Gospels and provides a straightforward account of the life and teachings of Jesus Christ.