Sabbath. Though I find it to be an Old Testament element fulfilled and realized in the person of Jesus Christ, the concept carries well into New Testament times. Not as a law that must be observed but as a healthy principle.
Being diligent to set time aside spiritually to be with God one-on-one is a much needed practice. It recharges one’s spiritual batteries and ensures a close relationship. It is easy to substitute Christian gatherings and even devotional practices for a personal time with Jesus, but quality time focusing on the Person of Christ alone is critical to proper growth.
Down time physically and mentally is an element is also a principle that can be gathered from the Sabbath. Taking time to relax can enable a person to take step back out of the cloud of busyness and constant physical output and come back with renewed clarity and energy.
Both the spiritual and physical/mental downtime can be taken too far so that one becomes spiritually lazy, ineffective & unfruitful (in the name of being “spiritual”) as well as out of shape, unproductive, sloppy, dulled, and lazy (in the name of “recharging”). But on the other hand it is all too easy to burn out or flame out by never taking a day off.