Exodus - Chapter 22

Another rule here - "You must give me the firstborn of your sons.  Do the same with your cattle and your sheep.  Let them stay with their mothers for seven days, but give them to me on the eighth day."

The first link to Jesus is found in Luke 2.  "On the  eighth day, when it was time to circumcise him, he was named Jesus."  This act of circumcision, was a demonstration of Jesus being given to God.

But there is another link to Jesus.  Jesus was the firstborn not only of Mary, but also of God the Father.  And as he rose from the dead on the first day of the week (which is also the eighth day, being the day after the seventh day of the week) he was effectively returned to the Father on the eighth day.