Matthew 6:34,
Therefore, do not be anxious about tomorrow, for tomorrow will be anxious for itself. Sufficiency for the day is its own trouble.

Early in the morning, Martha was so busy finding suits that she wanted to wear for the party that she was going to attend the next morning. She did her best to find her favorite dress that she bought in Paris, but she wasn't able to find it. She became anxious for tomorrow's event and forgot the things that she needed to do in the present day–attend her child's graduation. 

Though this story is only fictional, it serves as a lesson in life. 

It also happens during Sabbath day. On Sunday, we busied ourselves doing our tasks and requirements that we needed to pass on Monday, and we weren't able to go to church because of that.

We, as humans, are also like that. We are like Martha. We tend to keep worrying about the things that have not yet happened and forget the things that we need to do today for us to survive, which leads to being anxious in life.

This is also what God wants us to do; we should not be anxious about tomorrow instead of letting tomorrow be anxious about itself.