Leviticus 22:27
When a bullock, or a sheep, or a goat, is brought forth, then it shall be seven days under the dam; and from the eighth day and thenceforth it shall be accepted for an offering made by fire unto the LORD. When a bullock, or a sheep, or a goat, is brought forth, then it shall be seven days under the dam; and from the eighth day and thenceforth it shall be accepted for an offering made by fire unto the LORD.
It belongs to the laws governing sacrifices and offerings. A newborn bullock, sheep, or goat was to remain under its dam for seven days after birth. From the eighth day of its life onward it was eligible to be accepted for an offering made by fire to the Lord. That allowance from the eighth day and thenceforth did not require an offering on every eighth day thereafter.
Its details carry meaning that is found more fully in the sacrifice, life, and work of Jesus Christ. The offerings point forward to Him. The slain animals represent the Lamb of God who takes away the sin of the world.
Those who held the eighth-day teaching understood its mention of acceptance from the eighth day and thenceforth as a type and shadow of the eighth or first day of the week. In that understanding it typifies the first day to be the Christian Sabbath. It thus shows the Sabbath as still binding as given at Sinai but changed from the seventh to the first day, so that only one seventh part of time is required.