Cardinal number
From Sensus Plenior
At the end of day one, God says it was day one, using a cardinal number. On the rest of the days, he used ordinal numbers, as second, third, etc.
It is suggestive, as is Ge 2:5, that all of creation happened on one day.
The word for 'one' אחד also means 'go thee one way or the other.
- Eze 21:16 Go thee one way or other (אחד), [either] on the right hand, [or] on the left, whithersoever thy face [is] set.
When he called it 'Day one', he said, this is the day to choose whom you will serve.
