Why are we directed to ask for bread only ‘this day?’

It is the Lord’s teaching that we should not be anxious about the future, but place our trust in God: “Fear not, little flock, for it is your Father’s good pleasure to give you the kingdom… provide yourselves with purses that do not grow old, with a treasure in the heavens that does not fail… For where your treasure is, there will your heart be also” (Luk 12:29–34).