Gen 8:13 And the LORD said to Abraham, “Why did Sarah laugh, saying, ‘Shall I surely bear [a child,] since I am old?’ The word LORD in this scripture is Strong's 3068 YHWH which is God. The subject of Gen 18:1-15 is a child for Abraham and Sarah and in verse 1 "the LORD appeared" in person and there is a conversation with Abraham. There are too many scriptures in the Bible that point to the fact that the Son is not God which brings up the issue of how could God Himself appear to Abraham in person if He has never been seen? This is as close to any possibility of there being an error in scripture that exists in the Bible. 1John 4:12 No one has seen God at any time. If we love one another, God abides in us, and His love has been perfected in us.