The Bible teaches that Jesus lived, died, rose back to life, ascended to heaven (from where he now reigns and rules) and promised to come back to us at what is commonly called the Second Coming.
In 1 Thessalonians 4:13-18 the apostle Paul, the author of a large chunk of the New Testament, speaks about the Second Coming of Jesus.
For the Lord himself will come down from heaven, with a loud command, with the voice of the archangel and with the trumpet call of God, and the dead in Christ will rise first. After that, we who are still alive and are left will be caught up together with them in the clouds to meet the Lord in the air.
In Old Testament times there was no Facebook or Twitter. No email. Not even a telegram! (Do people even remember what a telegram is?) No bbm-ing to get together to start a riot or Facebook-ing to overthrow a government. When the priest wanted to gather God’s people together at the temple they had their own form of social media: the trumpet. When God’s people heard the trumpet they knew they were to gather for a feast or special occasion.
When a VIP (like the emperor or consul) paid an official visit to a city in the Greco-Roman world (the world in which the New Testament was written), the leading citizens would go out of the city to meet him and escort him on the final stage of his journey back into the city. This is the language and concept here.