"One of the best ways to avoid dealing with today’s challenges and difficulties is to get wrapped up in tomorrow’s. It seems easier to worry about what might not happen in the future than to deal with what is happening in the present! Tomorrow may require plans and forethought, but not worry. Today requires work and trust. Worry immobilizes us today and reveals a lack of trust in God’s ability to hold tomorrow and preserve us. Jesus left no doubt that troubles of one kind or another will be part of the daily routine. But he also described those troubles as “enough” for each day. Can we not also trust God to provide whatever we need for the day? When we worry about tomorrow, we misuse the strength God has provided for today. We need to take “one day at a time” in our relationship with God."
Bruce B. Barton, Matthew, Life Application Bible Commentary (Wheaton, IL: Tyndale House Publishers, 1996), 128.