Charles Spurgeon Commentary Numbers 9:15-16

"And on the day that the tabernacle was reared up the cloud covered the tabernacle, even the tent of the testimony: and at even it was upon the tabernacle as it were the appearance of fire, until morning. So it was alway: the cloud covered it, and the appearance of fire by night." — Numbers 9:15-16 (ASV)

This was the sign of the presence of God in the midst of that vast canvas city. I suppose that the great cloud rose up from the most holy place, and probably covered the whole camp of the tribes, so that it shielded them from the fierceness of the sun, while at night the entire region was lit up by this marvelous illumination. The chosen nation had the pillar of cloud by day for a shelter, and the pillar of fire by night for a light. God's presence acts upon us in much the same way as the cloudy fiery pillar acted upon Israel.

"He has been my joy in woe,
Cheered my heart when it was low,
And, with warnings softly sad,
Calmed my heart when it was glad."

We get shelter from the fierce heat of the world's day and deliverance also from the darkness of the world's night through our Lord's gracious presence.