After Abraham built an altar, he pitched a tent (12:7-8). At Babel, the people firstly built a city and then erected a tower. But Abraham firstly built an altar and then erected a tent. This means that Abraham was for God. The first thing he did was to take care of the worship of God, of his fellowship with God. Secondly, he took care of his living. The tent was for Abraham's living. Abraham did not take care of his living first. That was secondary. With Abraham, the primary matter was to consecrate everything to God, to worship and serve God, and to have fellowship with God. Only then did Abraham pitch a tent for his living. Abraham's dwelling in a tent indicated that he did not belong to the world but was a testimony to the people (Heb. 11:9).
Abraham firstly pitched his tent at the place between Bethel and Ai (12:8; 13:3). That was the place where God's house was and where he began his testimony in expressing God by fellowshipping with Him. His altar was the beginning of his testimony for God to the world, whereas his tent was the completion of his testimony to the world for God. His tent was a miniature of the tabernacle built by his descendants in the wilderness, which was called the "tabernacle of testimony" (Exo. 38:21). Since his tent was pitched by Bethel, in a sense it may be considered as the house of God for God's testimony on earth.
Later, Abraham removed his tent to Hebron, which means fellowship (13:18). His tent firstly was a testimony for God to the world and then it became the center where he had fellowship with God. This is strongly proved by what occurred in chapter eighteen when God came to stay with him in the tent at Mamre in Hebron. By Abraham's pitching a tent God had a place on earth where He could communicate and fellowship with man. His tent brought God from heaven to earth. All of us, God's called ones, should pitch a tent. On the one hand, such a tent is a testimony of God to the world; on the other hand, it is a place of fellowship with God to bring God from heaven to earth.
Do not think that this matter of a tent is a small thing. Later, when Abraham's descendants were called out of Egypt and entered into the wilderness, God commanded them to build a tent and in front of the tent He commanded them to build an altar (Exo. 26:1; 27:1). There, in Exodus, we see an altar with a tent, a tabernacle. That tabernacle was God's house on earth. Abraham's tent was also God's house on earth. In Genesis 18 we can see that God came and stayed with Abraham in his tent. At that time, Abraham was a priest offering sacrifices to God. His building an altar and offering sacrifices to God proved that he functioned as a priest. God's intention is that all of His called ones should be priests. We are priests. We do not need others to offer sacrifices for us. We must do it ourselves. When Abraham was feasting with God in his tent, he was the high priest, and the inner part of his tent was the Holy of Holies. God was there. By this we can see that Abraham's tent was a prefigure of the tabernacle built by Abraham's descendants in the wilderness as the dwelling place for God and for the priests. Here in Genesis we see a priest named Abraham who lived with God in his tent. At the side of this tent there was an altar.