From my reading, six convicting reasons for why it is sinful to worry. And just so you know I am very much talking to myself here and it reminds me of something I heard in a sermon about a year ago, "Worry is a sinful form of self-torture."
1. Worry is totally fruitless. Have you ever succeeded in adding an inch where you wanted it, or subtracting one from where you didn't want it, merely by being anxious? If you can't accomplish that by worrying, what can you accomplish?
2. Worry is worse than fruitless. It is disobedience. Note these commands:
Let not your hearts be troubled.
Be not dismayed.
Be of good cheer.
3. Worry is taking the not-given - for example, tomorrow. Tomorrow is not ours to worry about. We are allowed to plan for tomorrow, but not to worry about it. Today's troubles are enough of a burden. Jesus knew exactly what He was talking about when He said that.
4. Worry is refusing the given. Today's care, not tomorrow's is the responsibility given us, apportioned in the wisdom of God. Often we neglect the thing assigned for the moment because we are preoccupied with something that is not our business just now. How easy it is to give only half our attention to someone who needs us - friend, husband, or little child - because the other half is focused on a future worry.
5. Worry is the antithesis of trust. You simply cannot do both. They are mutually exclusive
6. Worry is a wicked squandering of time (as well as energy).