The first altar mentioned in the Bible is the altar that Noah built when he came out of the ark. There was a lot that went on before Noah came to that altar. God spoke to him about things not seen as yet, and Noah believed God and went on to do what God told him.
We have heard about the Lord’s coming and the Day of Judgment, and they are things that are “not seen as yet, but they are coming. Noah carried out the plan God had given him, and then he came to this altar. When he put the animals on the altar, it tells us that the Lord smelled a sweet savour. When the animal was slain and put on the altar, it would not have been very sweet then; it was the fire that released the sweet savour from the yielded life. The consuming fire of the love of God releases the sweet savour from a yielded life, not just when we first yielded our life.