From Grace Upon Grace: Spirituality for Today by John W. Kleinig, on saying grace before our meal:
“Because God provides us with our daily bread and all that we need for our physical journey on earth, we exercise our faith by saying grace before and after meals. This simple custom, this act of daily thanksgiving, acknowledges two profound realities. On the one hand, it acknowledges that we receive our food, like all our apparent possessions, as a gift from God for our nourishment and enjoyment. On the other hand, it also acknowledges that the triune God is the host of the meal who does not just provide us with food but also wishes to bless us by his presence with us. The saying of grace makes every meal a holy meal because it has been sanctified by the Word of God and prayer.” (56)
Now I understand the Common Table Prayer (“Come Lord Jesus, be our guest/And let thy gifts to us be blest”). It has to do with God’s presence at our meal!