Hallow means holy saint. So on the appearance this day sound like a good day to observe since there is nothing wrong with honoring the saints one day a year as long as you are not bowing down and worshiping them. The New Testament refers to Israelites who are in Christ as saints.
The Festivals of Parentalia, Feralis, and Carista
Feast of Purim
Later in the Book of Maccabees a decree was made to memorialize the 13th day of the twelve month, now called February, as a day to remember that they defeated their adversaries.
Therefore, now the Feast of Purim was to begin on the 13th day just like the feasts of Parentalia and Feralis which became the All Saints Day until it was moved to May. It was a day to remember all those who had died in the Book of Esther and it 2nd Maccabees.