והיו לך למקרא העדה, these trumpets were to be Moses’ personal property to be used to alert the congregation in times of need by blowing in them. A second purpose would be to alert the encamped Israelites to get ready to move on. מסע, the word is a noun similar to נסיעה.

את המחנות, as if the Torah had written למחנות, for the encamped communities.

ותקעו בהן, in both of them.

לחובב, another name for Yitro, as we know from Judges 4,11 מבני חובב חותן משה, “of the sons of Chovav, the father-in-law of Moses.”

כי על כן ידעת, while you have been with us in the desert you have become as indispensable as our eyes.

'מהר ה, for the people at that time had still not moved from Mount Chorev in the desert of Sinai. This was after the Tabernacle had been erected, as I have explained in connection with Numbers 1,1 on the words מדבר סיני.

דרך שלשת ימים, they walked for a period of three days, not making camp until the end of the third day. Seeing that this had been very strenuous, the people began grumbling, as we know from Numbers 11,1, a phenomenon which also occurred in the last year of their wanderings and is recorded in Numbers 21,4. At that point the mood of the people is described as ותקצר נפש העם בדרך וידבר העם באלוקים ובמשה, “the people’s soul was restive on the journey and they spoke out against G’d and against Moses.”

וארון ברית ה' נוסע לפניהם, during these entire three days, looking for a suitable place for them to make camp; for the cloud was seeking out such a location.

'קומה ה, seeing that during the period of their wanderings the Shechinah had been absent from its usual place above the kapporet.