The first mention of circumcision is in chapter 17 of Genesis have a look at verses 9-14
Does anyone know why it's the eight day that a male child is circumcised. Not the seventh or the ninth but the eighth...?? I thought maybe because no work can be done on the seventh perhaps? But its after the child is born and not according to any calendar
In Hebrew the number
eight [Sh'moneh) means "to make fat" or "to super abound."
As
seven means or indicates spiritual completeness, then
eight indicates that which is superabundant or satiating.
Adam was formed [not created] on the
eighth day as distinct from other humans, male and female, created on the
sixth day.
Jehovah's covenants with Abraham are
eight in all
Abraham's sons were
eight in number: seven were born after the flesh, while one the
eighth was the child of promise.
Consecration of Aaron and his sons was on the
eighth day, after abiding at the door of the Tabernacle day and night
seven days.
In Solomon's Temple there were
eight classes of furniture, while in the Tabernacle there were
seven.
The Sabbath to be kept holy: there were
eight commands in all,
seven by Jehovah; and
one by Moses.
David was the
eighth son of Jesse (1Sam 17:12)
Noah and his family saved on the Ark were
eight in number.
Eight is
seven plus
one hence it is the number specially associated with
resurrection and
regeneration and the
commencement of a new era or order.
Circumcision was to be performed on the
eighth day because it was the foreshadowing of the true circumcision of the heart,
that was to be made without hands; "the putting off of the body of the sins of the flesh by the circumcision of Christ."
Colossians 2:11 > new creation in Christ Jesus. buried with him and raised unto new life in him ...
The first born were to be given to Jehovah on the
eighth day (Exodus 22:29-30)
With thanks to
The Works of Ivan Panin on Bible Numerics ; and to
E.W. Bullinger 'Number In Scripture
Its Supernatural Design and Spiritual Significance' 
