Good manners are very important. As kids, my sister and I were taught to mind our manners, especially when we visited the homes of friends and relatives. We need to be reminded that prayer takes us to a different place. That place is God's throne of grace. When we are in prayer, we are in spirit, coming before the throne of God. We are elsewhere, and not just any where, we are before God. Therefore we should mind our manners.
POST SCRIPT: I was teaching a series of lessons about prayer for our mid-week children's ministry. Heb. 4:12 has been such a blessing.