I know it has been difficult to see, but the book of Numbers thus far has been preparing you for the continued journey of Israel from Sinai. We began with God’s selection of leaders in every tribe (Chapter 1). In chapter 2, the tribes (except for that of Levi) were arranged around the tabernacle of the Lord. There are three tribes on each side, and a lead tribe for each three. God also prescribed how each of these tribes were to move out.
In Chapters 4-5, the tribe of Levi was arranged. In chapter 9, we are informed as to the guiding light for God’s people: it is to be God Himself, seen in a cloud by day, and fire by night.
When the cloud moves, God’s people move.
In Chapter 10, God provides for the signal to move. It was likely too much to expect that Israel would keep her eye on the fire or cloud, so the signal that a move was underway was created by special trumpets and special soundings. The trumpets were used by God to sound a move, to call meetings, and to go to war. They were God’s trumpets, and the image we get here is one of Israel, listening for the trumpet call of God.
I think it is neat how this imagery is carried into the New Testament. Christians are waiting for the call of God (1 Thessalonians 4:16), whose voice is like that of a trumpet (cf. Revelation 8-11).