‘And when Abram was ninety nine years old Yahweh appeared to Abram and said to him, “I am El Shaddai (God Almighty). Walk before me and be perfect and I will make my covenant between me and you and will multiply you greatly”.'
Again the number is significant. It indicates that the miracle heir will be born when Abram is ‘one hundred', in other words at God's perfect timing.
(Note however that Abraham can at the same time describe himself as ‘a hundred years old' (Genesis 17:17 - compare Genesis 17:24). We must not tie the ancients down to our exact methods of using numbers. They indicated a different thing by them).
“I am El Shaddai” - ‘God Almighty' - the One Who is ‘competent' to perform what He promises. Previously God's covenant has been with His chosen people as Yahweh. But now He will make a covenant that includes other peoples and other nations. To them therefore He is El Shaddai, ‘God Almighty'. Previously every covenant has been from ‘Yahweh', and very personal, now Yahweh reveals Himself as not just Lord of one nation but of many nations.
This has, of course, been implicit in what has been revealed to Abram previously, but now it is made explicit. He is not only Yahweh, their personal God, but El Shaddai, God over all. He will not only govern the destiny of the chosen nation but of other related nations too to whom He will not be known as Yahweh. This will include the descendants of Ishmael, and also later of the Edomites and the sons of Keturah (Genesis 25:1 on). And to ratify this covenant an outward sign that can be seen by all nations is introduced, circumcision on the eighth day.
“Walk before me and be perfect ---”. Enoch and Noah walked with God (Genesis 5:22; Genesis 6:9). Those were days when the presence of God was more intimately known than now. Now Abram can only walk before God as God watches over him. Being ‘perfect' means walking within the covenant stipulations, fulfilling all God's requirements, being a faithful liegeman (compare Deuteronomy 18:13).
“I will make my covenant with you ---”. Abram is already a man of the covenant. But the birth of Ishmael indicates the necessity for a wider and broader covenant. Abram has failed in faith and pre-empted God. Now God calls him back to obedience and will establish a wider covenant which will include Ishmael and his promised seed. Of course, while Ishmael is with the family tribe Yahweh watches over him. But once he leaves he will come under the provenance of God as El, -- El Roi (Genesis 16:13), El Shaddai.
Here the impression given is that it is Abram's obedience that will result in the blessing. But we must not forget that the blessing has already been guaranteed in response to Abram's faith (Genesis 15:6). Thus we have the perfect example of the fact that God's covenant is made with us as a gift of grace in response to faith, but that as a result obedience is expected through which the blessing will be received. Genuine faith will always produce obedience (‘works').
As in Genesis 15 Abram is the passive receiver of the covenant. It is Yahweh, El Shaddai, Who determines its content and promises. It is the Great King Who speaks to His liegeman. And yet Abram is more than a liegeman, he is the chosen of Yahweh.