In Deuteronomy 16:1, the word 'Passover' is out of context. It applies to the whole season, including the Night to be Much Observed and the Days of Unleavened Bread.
Deuteronomy 16:1-8 refers to Unleavened Bread rather than Passover (a scribal error, perhaps referring to the season). Ten clues clear up this misconception.
The context of Deuteronomy 16:1-3 indicates the focus of these verses is on the Night to be Observed and the Days of Unleavened Bread rather than the Passover.
At the time of Christ, because of historical deviation, some kept Passover at home at the start of the 14th and others kept it at the Temple at the end of the 14th.
The temple Passover commanded by Hezekiah was a very unusual circumstance in which the king centralized worship to keep Baalism from defiling the Passover.
Major reinterpretations have significantly distorted the meaning of Passover and Unleavened Bread, blurring the distinction between the two events.
Passover takes place at twilight as the 14th of Abib begins. Unleavened Bread begins 24 hours later on the 15th of Abib. The Passover is a preparation day.
The Night Much to be Observed is a memorial of the covenant with Abraham, and God's watchfulness in delivering ancient Israel as well as spiritual Israel.
The term 'selfsame day' refers to the covenant God made with Abraham 430 years before the Exodus, which occurred on the day after the Passover.