the man who values a particular day does so to the Lord. The eater eats to the Lord, since he thanks God for his food; the non-eater abstains to the Lord, and he too thanks God.
Then he took a loaf, and after thanking God he broke it and gave it to them, saying, "This means my body given up for your sake; do this in memory of me."
Then he ordered the crowds to recline on the grass, and after taking the five loaves and the two fish he looked up to heaven, blessed them, and after breaking the loaves handed them to the disciples, and the disciples handed them to the crowds.
Otherwise, suppose you are blessing God in the Spirit, how is the outsider to say 'Amen' to your thanksgiving? The man does not understand what you are saying!