I believe one of the primary reasons believers should get together is to exhort one another. Basically, we need accountability. The Holy Spirit testifies to us who God is. When believers are around each other, they can encourage each other, admonish one another, remind one another and advise one another.
Let us hold fast the confession of our hope without wavering, for He who promised is faithful. And let us consider one another in order to stir up love and good works, not forsaking the assembling of ourselves together, as is the manner of some, but exhorting one another, and so much the more as you see the Day approaching. Hebrews 10:23-25 NKJV