“On the eighth day,

They came

To circumcise

The child.

Καὶ ἐγένετο ἐν τῇ ἡμέρᾳ τῇ ὀγδόῃ ἦλθον περιτεμεῖν τὸ παιδίον,

Luke explained what happened on the eighth day (Καὶ ἐγένετο ἐν τῇ ἡμέρᾳ τῇ ὀγδόῃ) after the birth of the child.  They came to circumcise this child (ἦλθον περιτεμεῖν τὸ παιδίον).  This circumcision, brit milah, or bris was a sign of the covenant with God that goes back to Abraham in Genesis, chapter 17:11-12.  This sacerdotal covenant alliance story emphasized male circumcision as the main part of the Yahweh covenant.  Thus. circumcision became a big deal.  Every male was to be circumcised by removing the flesh of the foreskin of his penis, when he was eight days old.  This also included male slaves born or brought into the house.  An uncircumcised Jewish male would be cut off from his people, because he had broken the covenant with God.  Circumcision has been practiced among many ancient and contemporary groups for either religious or hygienic reasons.  In fact, despite their differences, Islamic males practice circumcision also.  In the USA, most boys born in a hospital are circumcised for hygienic or health purposes.