Well, let me try to explain this in layman's terms, to eliminate the mystery (as we are not privy to all God's knowledge), if possible. Obviously, God is love....love is not possible if there is nothing, or no one, to love. So, God's three distinct personalities gives us some insight into God's love. This love was shared prior to his creations between the father, the son and the Holy Spirit.

Genesis 1:26 Then God said, “Let Us make man in Our image, according to Our likeness..."

Hopefully, this makes sense to those who can't make sense of something beyond our finite grasps.