Abraham and Circumcision

I have been reading through Genesis and just recently came to chapter 17 when God covenants with Abraham and gives him the rite of circumcision. Below is a copy of an email sent to a dear friend:

In Chapters 12 and later 22, God promises to Abraham that his "seed" would
bless the nations. Then, in chapter 15, he tells him that for four generations after his "seed" goes into Egypt, then they would return to the land. There is a drama going on here, the "seed" who would crush Satan's head is expected (Gen 3:15). Every newborn child has the expectation of being this one. Cain is a child from the Lord, but then he is cursed by God, but God gives another son, Seth. All the people of the earth are destroyed in the Flood, but God saves Noah and his three sons, one of which is
cursed--actually his grandson Canaan, and one is blessed Shem. Then Abraham
is blessed, but he has no heir, then along comes Ishmael. Every new story is
an addition to the drama, but in chapt 17/18 God gives a glimpse of the future, His promise would not fail, the seed to come would not be Abraham, nor Isaac or Jacob or the patriarchs. It would still come but later. God always points the one whom he renews the covenant with, and the reader, to the future. There is still future hope. We must have the faith of Abraham (Gen 15:6). Also notice the covenant to Abraham, it is an eternal covenant, but the covenant is not circumcision.

Circumcision is a sign of the covenant, much like the rainbow was the sign of
God's covenant to not flood the earth. God's promise would prevail. Only, the
sign of circumcision had to be obeyed. Else man violated God's covenant. God
could not violate his own covenant, it was sealed by an oath. Check the book of
Hebrews here. Many people see the Abrahamic covenant as solely related to
circumcision, this is not the case. The covenant was deeper, circumcision
pointed to the covenant.

I was amazed at the introduction of the "sign" theme in chapter nine. Actually,
it was already introduced in chapter one, the heavens being signs for the times
and seasons. Then in chapter 17, circumcision is a sign. I became interested in
the theology of "sign" while studying Isaiah (see 7:14; 37-39; 66:18, only a few
of the many references to sign). Signs are used by God to show his faithfulness
to his covenants, but also to point the people to the past (rainbow to the
flood) or to the future (spreading of God's glory to the nations), but also to
both (circumcision to God's covenant with Abraham that would be fulfilled in the
future in the blessing of all nations through his "seed" (singular in Ch
22). See my buddy Dougald on the collective noun zerah.

In what way is circumcision a sign? Well, I will continue this discussion later. I think this is going to relate to the discussion of Colossians 2:11-12 started below