The Ten Commandments tell us that there is one day of the week to cease work and to dedicate to God. The Bible tells us in Genesis that even God rested on the 7th day.
This wisdom is of much use to us today as it was in the days of Moses.
Negative energy (here meaning stress, anger and bad feelings) gather as we work and interact with the world. One who does not take the time out to get rid of these will even find himself becoming physically ill.
In martial arts training this is also true. I actually saw in an episode of Street Fighter- Assassin's Fist (Episode 3 on Youtube if you haven't seen the series yet) that Gotetsu told his students to "cleanse their spirit" with meditation after training.
Beside physical exertion- your training will also put stress on your mind and anger and frustration can easily set in. This is harmful.
Meditation serves to restore balance and to rid ourselves of the mental clutter from training. Shaolin students will further tell you that it restores energy as well.
Wenhsiuquan relies on meditation as one of its cornerstones.
If you have any questions about meditation you can contact me at firstname.lastname@example.org