Lent is a season in the Church that is marked by prayer, fasting, almsgiving and repentance. This is the season that is very popular among clergy types, mainly because it encourages everyone to do things that clergy types desire people to do throughout the year - Lent just makes these things socially acceptable.
There are more than enough posts and resources that explain the significance of the 40 days of Lent (or more, depending on who is counting). There is all sort of traditional and biblical connections to the number 40 and those are rich metaphors to consider when thinking about Lent. But there are many significant numbers in the tradition and Bible (basically the numbers 1-42, 50, 70, 120, etc.). So why 40 for Lent? Why not 12 days? Why not 30?
Perhaps the reason Lent needs to be 40 days is because that is how long it takes to move into the desert of our souls and wrestle with our demons. The ancient Desert Christians thought that going into the desert was literally where the demons lived. As such, they would go out in order to 'battle' these demons on behalf of others. Demons are tricky, they can hide very well from us and maybe this is why the desert Christians did not feel they could wrestle with demons while still living in town. It takes a while to find demons, it makes sense to move in and dwell on their 'turf'.
Because our demons are masters of disguise in order to find them we have to unmask a lot of who we are. This task takes time. It is difficult to unmask all parts of ourselves to discover what is our true self and what are the demons lurking in us, wreaking havok. Forty days may be the amount of time it takes to do such work.
Everyone starts a Lent fast strong, but after a few days (as we move closer to our inner demons) the fast gives way. We forget why we embarked on this task to begin with and it it just easier to let the masked remain. May we fight the good fight and wrestle with our demons for these 40 days.
It may also be worth noting that the desert Christians not only believed the desert was were the demons lived, but it was also where the angles lived. Just as the presence of God was with Moses, Jacob and Jesus in the desert, so too God will be with us in our desert time.