In Jain practice, 7 Navkars before sleeping and 3 Navkars after waking up are generally done as a simple daily discipline to keep the mind connected with the Navkar Mahamantra at the two most important transition points of the day.

Why before sleeping?

• To end the day with remembrance of the Panch Parmeshthi.
• To calm the mind, reduce attachment to the day’s activities, and prepare for rest with spiritual awareness.
• It is a way of doing pratikraman-like inner reflection: remembering purity, humility, and forgiveness before sleep.

Why after waking up?

• To begin the day with shuddh bhav and devotion.
• To remind oneself first thing in the morning of the ideal of Arihants, Siddhas, Acharyas, Upadhyayas, and Sadhus.
• It creates a spiritual tone for the whole day.

Why 7 and 3 specifically?

This is mostly a customary devotional practice, not a universal strict scriptural rule for everyone. Different Jain families and traditions may follow different counts. The idea is:

• 7 before sleep: a slightly longer closing remembrance
• 3 after waking: a brief, focused opening remembrance

Main purpose

The real importance is not only the number, but the bhav:

• faith
• humility
• purity
• awareness of the soul
• remembrance of the Navkar Mahamantra

So, these counts are a practical discipline to bookend the day with Jain remembrance and right भावना.

If you want, I can also explain the spiritual meaning of each of the 9 words of Navkar Mantra.