Before moving on I should say that the promise to make Abram’s name great is not a part of the covenant oath which God takes in Genesis 15. It is worth noting that a covenant then is more than just a promise. God can promise something without including it within a covenant. As we shall see, a lot of confusion has come about by Bible teachers not taking care to differentiate between a promise of God within a covenant oath and a promise not housed within an oath.
The second part of Genesis 12 concerns Abram’s lack of faith and its fallout. Although descending into Egypt and promoting a lie concerning Sarai (12:11-19), God averted the dire consequences of Abram’s decisions, and at the beginning of the next chapter we find him living in the south part of the Promised Land. The ensuing story of the separation of Abram from Lot is not just the rehearsal of a necessary parting of the ways. Despite the sermonic grist found in the deference shown by Abram to his nephew, Dempster is certainly right to point that his offering a choice to Lot about where to live threatened the promise. Still, verse 14 notes that it was “after Lot had separated from him”, that God invited Abram to survey the land “for all the land which you see I give to you and your descendants forever” (13:15). The Lord then repeated His promise about those descendants being great, at least in terms of number (13:16). Although I do not think we should designate these Divine utterances by the word “covenant”, at least until chapter 15, it should be noted that in repeating His promises to the man He called out of Mesopotamia, God is reiterating His intention to do precisely what He told Abram He would do.
Before we can turn to the enactment of the Abrahamic covenant in Genesis 15 we must pause to describe the meeting between Abram and Melchizedek in chapter 14:18-20. Melchizedek is the king of Salem (which would become Jerus – salem), and he just appears as “the priest of God Most High” (El Elyon). Abram is returning from victory over the five kings who invaded Canaan, taking Lot captive. His meeting with the king of Salem is not described as a shock meeting. The narrative gives the impression that the two men knew each other. Melchizedek acts as the priest of God to bless Abram, and it is in that role that he receives tithes from Abram. We may wish to speculate about why Abram’s interactions with Melchizedek are not given more extensive coverage, but we must be satisfied with the little we have got. Those three verses are referenced by the writer of Hebrews to make several important points. Prior to speaking directly of this ancient king, his priestly role is spoken of via references to Psalm 110:4. The writer ties in the High Priestly function of the Risen Jesus with the Melchizedekian priesthood. In doing so he makes the point that this priesthood is superior to the Levitical one which would be instituted later under the Mosaic covenant (Heb.7:4-19). For one thing it is everlasting, and for another it is linked to “a better covenant”, the New covenant in Christ’s own blood. Even the name Melchizedek, and his title, king of Salem, are not passed over, but the author of Hebrews stops to mention that his name means “king of righteousness”, and his title, “king of peace” (7:2), showing that these adumbrate Christ’s future role.
The coincidences which the NT writer picks up on look upon a second glance to be arranged. Here we have a priest of God who appears on the scene to be almost forgotten by the time the Levitical cultus is established in the Book of Exodus. But this man is situated in what would become God’s city, Jerusalem (city of peace or foundation of peace), and he officiates, at least for a time, as the priest of God in Abraham’s day. More must be said about him, but it is enough to note that his possession of this priesthood gives Christ a non-Levite priesthood to step into in His mediatorship of the New covenant. Further, it may indicate that just as Jesus assumes Melchizedek’s priestly role, He will also one day assume his kingly role over earthly Jerusalem, thus bringing the throne and the priesthood together as indicated in Zechariah 6:12-13.
 I want to notice that the name ‘Abram’ was not the name which God would make great, but the revised name ‘Abraham.’ That said, it does not mean that God is in any way misleading him, for: 1. It was the same person to whom God promised a great name, 2. The expanded name is clearly related to the first, and 3. God told Abraham that it was under that name that he would henceforth be known. It wasn’t left up to the ingenuity of later interpreters to make the connection.
 Stephen G. Dempster, Dominion and Dynasty, 78
 Cf. William J. Dumbrell, The Search for Order, 35
 This is unusual in a book filled with genealogies. I take this to be what is meant by the cryptic language of Hebrews 7:3.
 See Hebrews 5:6, 10, & 6:20