Here is Jude, younger brother of the apostle, James, leader of the Judaistic inclined Jerusalem church. He is mentioned in John 14:22, questioning his ‘brother’ but not after the flesh, the Lord Jesus.
Jerome says he was sent to Edessa (of which there is a discovered ‘lost’ book of the New Testament. This King wrote to Jesus requesting He visit him. Jesus actually wrote a reply (i have it in print). He said He would send someone after He had been received up into heaven. He sent Jude, with gifts of healing him as well. He sent Jude. The book is not to one church or individual. He states emphatically that evil men have crept in among people of God. As today. As there are many mentions of Old Testament events, it could be sent to mainly Jews but personally I doubt that as many in the Early Gentile church had access to the manuscripts of the Septuagint and read them, according to historians. The intruders were heretics in doctrine, the major attack by Satan always, as today and specially after A.D.70 and probably A.D.63 at Paul’s martyrdom. He speaks of a contention between Michaelk, Archangel and Satan over the body of Moses. That could be one reason Moses appears with Elijah on the Mount of Transfiguration. when Jesus was transfigured before Peter, James (not Jude’s brother) and John, the latter two being the sons of Zebedee and Salome (sister of Mary). V.10 ‘Irrational animals; Gk. implies the mere perception of the animal senses and faculties. There is no spiritual knowledge at all..