A.T. Robertson Commentary Matthew 6:34

"Be not therefore anxious for the morrow: for the morrow will be anxious for itself. Sufficient unto the day is the evil thereof." — Matthew 6:34 (ASV)

For the morrow (εις τεν αυριον). The last resort of the anxious soul when all other fears are allayed. The ghost of tomorrow stalks out with all its hobgoblins of doubt and distrust.