Because just as the Messiah fulfilled all the spring appointed times of the Torah in his first coming, such as Passover of the Torah with his death on the day and hour of the Passover, first fruits of barley of the Torah with his resurrection on the day of the first fruits of barley, and Pentecost of the Torah 50 days later by sending his anointing on the day of Pentecost, so at his second coming he will fulfill the autumn appointed times of the Torah, beginning with the trumpet blasts, which is the first appointed time of the Torah in the autumn, which is why his second coming is associated with trumpet blasts, for they are the 7 trumpets of Revelation, which happen in correlation with the trumpet blasts of the Torah that happen in New Moon 7 Day 1, which is why we know the precise day and hour of the second coming, for according to Revelation he comes 1/2 prophetic hour before the first trumpet blast, which is 7 and 1/2 days.
This is because the Master himself will come down from heaven with the signal of a shout by the head angel and a blast of the trumpet of God. First, those who are dead in the Messiah will rise. Then, we who are living and still around will be taken up together with them in the clouds to meet with the Master in the air. That way we will always be with the Master.
1 Thessalonians 4:16-17
Then will appear the sign of the Son of Man in heaven. And then all the peoples of the earth will mourn when they see the Son of Man coming on the clouds of heaven, with power and great glory. And he will send his angels with a loud trumpet blast, and they will gather his chosen from the four winds, from one end of the heavens to the other.
Matthew 24:30-31