When you neglect fellowship you neglect to get your sword sharpened. Sword sharpening is very important in the life of a follower of Christ.
Of course, our sword is the Word of God. In the Armor of God, the Sword is the only defensive part of the armor.
When we fellowship, we can get our sword sharpened. That means learning from others and sharing with others what we know.
Iron sharpens iron,Proverbs 27:17
So one man sharpens another.
That fellowship helps to sharpen us and our fellow brothers and sisters. That is why Small Groups / Sunday School is important.
Not only do we learn and teach with others