Why did some Sufi orders require disciples to complete a 40-day period of seclusion?

In the context of Sufi orders, the 40-day period of seclusion—often referred to as chilla—was a common practice required of adepts as part of their rigorous spiritual training.1

This period of isolation under difficult conditions served as a means for the disciple (murīd) to undergo intense ascetic discipline. By withdrawing from the distractions of daily life, the seeker could focus entirely on the path (ṭarīqah) toward God, engaging in constant struggle against the lower soul and dedicating themselves to meditation and the remembrance of God (dhikr). This practice was intended to facilitate the disciple's spiritual transformation, helping them progress through various stations (maqām) and states (ḥāl) on their journey toward interior knowledge and, ultimately, the goal of annihilation in God (fanāʾ).21