What does Genesis 12:7 mean?

Abram believed God's promises to him (Genesis 12:1–3). He obeyed God's call to leave his home and travel to another land (Genesis 12:1–5). Now, after Abram and his large contingent have traveled to the heart of the land of Canaan, the Lord appears to him.

This is apparently a different experience than when God spoke to Abram in verse 1. The Lord "appears." We are not told what form He took. The Lord is called Yahweh, and the term used for when Yahweh physically appears to people is theophany. This is the first of several theophanies made to the fathers of Israel.

Yahweh brings a short, specific promise for Abram: I will give this land to your descendants. This is the first time God has promised the land of Canaan to the people who will become Israel. After leaving his old life, and his old culture, Abram was now home. Abram himself would not take possession of the land in his own lifetime, however. Even his descendants will not fully possess the land for several generations. But the promise had been made by God. It would happen.

Abram responded in the way that many people in Scripture do after being visited by the Lord. He built an altar. He may well have made an animal sacrifice, though that is not mentioned. It's possible that Abram's altar at Shechem stood as a reminder of this visit from the Lord for many years to come.