Father, sorry for the possibly silly question, but adding up the days from Ash Wednesday to the Lord’s Supper Mass, excluding, it does not add up to 40 if we exclude Sundays as memorials of the Resurrection, but 39 instead. So, how do we count Lenten days?
First of all, 40 is an important symbolic number in Scripture. Hence, the season is associated with Biblical “40s”.
40 shows up many times in Scripture, usually concerning a period of testing. For example, when God flooded the earth for 40 days and 40 nights. After killing an Egyptian, Moses spent 40 years in the deserts of Midian. Moses spent 40 days and 40 nights was on Mount Sinai. He interceded for the People for 40 days and 40 nights. The Israelites wandered in the wilderness for 40 years. Israel was enslaved by the Philistines for 40 years. Goliath taunted Saul for 40 days. Elijah traveled 40 days and 40 nights to Mt. Horeb. 40 also appears in various OT prophecies.
And of course Our Lord spent 40 days and 40 nights fasting and there were 40 days between His Resurrection and Ascension.
However, as far as Lent is concerned, in the ancient Church Lent began with what is now the 1st Sunday of Lent, that is, six Sundays out from Easter, and it ended on Holy Thursday, with the Triduum. That brings us to 40 days.
Because all Sundays, including those during Lent, are considered to be echoes of Easter, when we don’t do penance, Lenten Sundays were excluded from the count. That takes us down to 34 fast days. Ash Wednesday with Thursday, Friday and Saturday were added. As a result, between Ash Wednesday and Holy Thursday we have 44 days. However, subtract the intervening Sundays, and add back Good Friday and Holy Saturday and you wind up with 40 penitential days again.
There are different ways to tweak the number. However, the important point is the association with Biblical 40s, especially the time that the Lord spent fasting in the wilderness as His public ministry began.