In chapter eighteen, after Abraham believed and was circumcised, his fellowship with God became more intimate. This shows that he was indeed a friend of God. Genesis 18 is a special chapter. This chapter speaks of three things: (1) fellowship, (2) knowledge, and (3) intercession. These three things are intimately related, and they are the special enjoyment of a Christian who has been following the Lord for many years. We can only cover them briefly.
"And the Lord appeared unto him in the plains of Mamre" (Gen. 18:1). At the end of chapter thirteen, Abraham was dwelling by the oaks of Mamre, which was in Hebron. Hebron means fellowship. For God to appear to Abraham meant that Abraham was standing on the ground of fellowship. "And he sat in the tent door in the heat of the day; and he lifted up his eyes and looked, and, lo, three men stood by him" (18:1-2). This is a very peculiar portion of the Old Testament. God visited Abraham, not as the God of glory, but in the form of a man. It was as if He came to Abraham in plain clothes. God's appearance was fully in the position of a man. Therefore, Abraham did not feel that it was God who appeared to him. "And when he saw them, he ran to meet them from the tent door, and bowed himself toward the ground, and said, My Lord, if now I have found favor in thy sight, pass not away, I pray thee, from thy servant: let a little water, I pray you, be fetched, and wash your feet, and rest yourselves under the tree: and I will fetch a morsel of bread, and comfort ye your hearts; after that ye shall pass on: for therefore are ye come to your servant. And they said, So do, as thou hast said. And Abraham hastened into the tent unto Sarah, and said, Make ready quickly three measures of fine meal, knead it, and make cakes upon the hearth. And Abraham ran unto the herd, and fetched a calf tender and good, and gave it unto a young man; and he hasted to dress it. And he took butter, and milk, and the calf which he had dressed, and set it before them; and he stood by them under the tree, and they did eat" (vv. 2-8). This was Abraham's fellowship with God. Abraham was led by God to the point where he could communicate with God as a friend!
Then the subject of the son was brought up once more. Chapter seventeen speaks of Abraham laughing. Chapter eighteen speaks of Sarah laughing. Abraham was ready; he could communicate with God. While they were conversing outside the tent, Sarah was listening in the tent door, and while they were speaking to one another, Sarah was laughing within herself. God pointed out Sarah's laughing (vv. 12-15). This was fellowship. God became a man and communicated with a man. This is the fellowship between God and His people.
"And the men rose up from thence...and Abraham went with them to bring them on the way" (v. 16). This is fellowship. This is being God's friend. Once there is fellowship, there is knowledge. This kind of knowledge is not just the knowledge of the Bible but the knowledge of God. When Abraham fellowshipped with God, he acquired a knowledge of God. "And the Lord said, Shall I hide from Abraham that thing which I do?" (v. 17). What a word of intimacy! God was treating Abraham like a friend. Then God said, "Because the cry of Sodom and Gomorrah is great, and because their sin is very grievous, I will go down now, and see whether they have done altogether according to the cry of it, which is come unto me; and if not, I will know" (vv. 20-21). This means that God revealed His secret to Abraham. Before the Lord, Abraham was able to know what other men could not know. God's will is revealed only to those who walk with Him. The preciousness of walking with God lies in the fact that we can know God.
After God told Abraham of this secret, Abraham immediately entered into a work of intercession. Intercession is governed by fellowship; it is also governed by knowledge. With fellowship there is knowledge, and with knowledge there is the burden for intercession. The prayer that Abraham offered was a prayer that issued from his knowledge of God and his sympathy for God. Abraham drew near and said to the Lord, "Wilt thou also destroy the righteous with the wicked?...Shall not the Judge of all the earth do right?" (vv. 23-25). Abraham stood on God's side to pray; his prayer was fully on behalf of God's righteousness. In other words, his prayer was not to move God's heart but to express it. Hence, a prayer that knows God's heart is not a prayer that changes His will, but one that expresses His will. Abraham's prayer was a prayer that knew God's will; it was a prayer that expressed God's will. He was truly God's friend!