In the book of Genesis, we see that God(YHWH) comes and speaks to Abraham. God tells Abraham that he will have a son by Sarah in one year and that He is about to pronounce judgment on Sodom. In this account, God appears to Abraham as a man. We are told that 3 men show up to speak to Abraham. Two we know are angels as they go off to Sodom and warn Abraham's nephew Lot about the impending destruction of the cities of the plain. The third man is clearly identified as YHWH(YEHOVA) by Moses, rendered as LORD in our English translations. This account, together with the words of Christ Himself prove that Jesus appeared to Abraham and that Jesus is indeed God.
Abraham worships the man who visits and the man accepts the worship, proving that the man is God. When Moses spoke to God in the burning bush, Moses asked God what His name was. God's response was, "I AM that I AM , YHWH is my name." Moses, who wrote the Genesis account, identifies the man who came to Abraham as YHWH. So we can connect the dots that Moses identifies God as I AM and YHWH. We also see that God has appeared to Abraham as a man.
Christ, during His ministry, walked the earth as a man. Jesus specifically taught the disciples that the Father is Spirit. Abraham met God in the form of a man. When the religious leaders began to question Jesus about His authority He responded by saying, "you claim to have Abraham as your father... before Abraham was I AM." The religious leaders knew exactly what Jesus was saying as they picked up rocks to stone Him because they considered His words blasphemy, that a man should claim to be God.
Moses emphatically demonstrates that the third man who came to Abraham was God in human form. Moses also ensures the reader understands that I AM and YHWH are one and the same. When Jesus declared "before Abraham was, I AM" it leaves no doubt that Jesus is the man who appeared to Abraham.
God's plan of redemption was always in sight. Back at the Garden of Eden, God declared His plan to save mankind and to destroy Satan in Genesis 3:15. As Jesus appears to Abraham and reveals to him that he will be a blessing to all nations, He has the cross in sight. God began laying the groundwork for man's redemption as soon as man sinned in the Garden. God continued to reveal His plan throughout Israel's history and pre-history in the case of Abraham. That is the love of God that He became a man to die for men who rebelled against Him. That's how much God loves you!