What does Genesis 28:15 mean?

The Lord is communicating with Jacob in a dream, as he rests his head on a rock in the wilderness (Genesis 28:10–14). In the dream, Jacob sees God standing at the top of a ladder-like structure reaching from earth to heaven. In the previous verse, the Lord spoke to Jacob the very same promises He had made to Abraham. He would give Jacob's descendants this land. Those descendants would be as the dust of the earth spreading out in every direction. And through those descendants, all the peoples of the earth would be blessed.

Now the Lord gives to Jacob promises that are especially for him in this journey he is taking out of the land of Canaan. The Lord promises to personally be with Jacob wherever he goes, even into Mesopotamia. He also promises to bring Jacob back to the land of promise. Finally, the Lord promises never to leave Jacob until His other promises are fulfilled.

It's easy to read past these "be with you" promises, but the Lord knew that Jacob needed to hear and believe them. Traveling from his home to a strange place to begin a new stage of his life, and seemingly alone, it would have been easy for Jacob to forget the larger purpose of his life and live in fear. The fact that the Lord was with him in every step and had a definite plan for his future should give meaning and confidence to anyone.

In a similar way, God's promises to never leave or forsake those who trust in Christ should help us to overcome our fearfulness about the future (Hebrews 13:5–6).