Exodus 33:2
And I will send an angel before thee; and I will drive out the Canaanite, the Amorite, and the Hittite, and the Perizzite, the Hivite, and the Jebusite: And I will send an angel before thee; and I will drive out the Canaanite, the Amorite, and the Hittite, and the Perizzite, the Hivite, and the Jebusite:
The words were spoken in the aftermath of Israel's sin at Sinai with the golden calf. They promise that an angel will go ahead of Israel and drive out the Canaanite, the Amorite, the Hittite, the Perizzite, the Hivite, and the Jebusite from the land promised to Abraham, Isaac, and Jacob. The promise of the land and its abundance remained despite Israel's perversity.
At the same time the verse declares that God Himself would not go among the people in their midst on their journey. The reason was Israel's stiff-necked stubbornness and rebellion. His presence among them was a danger, lest their further waywardness provoke His wrath and judgment and He consume them on the way.
The angel's leadership and the promised abundance did not mean that God was accompanying Israel. Nor could Israel safely separate from God, for victory depended on the Lord Himself going with them. On hearing this, the people mourned, removed their ornaments, and sought mercy. The tent of meeting was placed outside the camp, and Moses interceded for them.