The Last Great Day is called the “eighth day” in Leviticus 23:36 and 39 since it immediately follows the Feast of Sukkot (Tabernacles).

The eighth day is a separate Holy Day that has a separate convocation. Just as many have mistakenly considered Passover to be a part of the Days of Unleavened Bread, many have mistakenly considered the Last Great Day to be the final day of the Feast of Sukkot (Tabernacles). However, to teach or accept this is contrary to the Scripture.

2 Thessalonians 1:11-12 HNV

To this end we also pray always for you, that our God (Yehovah) may count you worthy of your calling, and fulfill every desire of goodness and work of faith, with power; that the name of our Lord Yeshua may be glorified in you, and you in him, according to the grace of our God and the Lord Yeshua the Messiah.