The adjective “servile” refers to the quality of something being slave-like. Generally speaking, keeping holy the Lord’s Day means taking time for spiritual matters (for Catholics, that would mean the obligation to attend Mass,) and for such family, intellectual, cultural, recreational or social activity that would be restorative to one’s soul and psyche. This could even include something like doing some gardening or household repairs or maintenance, particularly if you’re approaching it as a hobby and not as something onerous. You really are supposed to use the day to help maintain human relationships as well, so holing up with statistics by yourself might be a little negligent of family obligations, for example, if you’re doing this for hours on a Sunday.
God knew we had to have time off to praise Him, and to restore our bodies and souls. If you read through the entire text of the Ten Commandments, you will notice that the commandment to keep the Sabbath holy goes on at some length to prohibit exploitive work done by “your slave or your maidservant, your ox…” And Jesus Himself states, “Man was not made for the sabbath, but the sabbath was made for man.”
So while worship of the Lord is the primary duty of the Sabbath, it seems that we have a duty to ourselves and to others to refresh ourselves mentally, emotionally, and physically as well as spiritually. In other words, it’s a real good idea to get some balance in life by taking a break every week. It’s such a good idea that God decided to order us to do it.
Some people, who work in positions necessary for the common good (i.e., medical personnel, emergency workers, and the like,) must necessarily work on Sundays and incur no sin for doing so. Most parishes have an anticipated vigil Mass that would fulfill their Sunday obligation. Plus, I’ve always wondered how priests approach the entire idea of sabbath, since they obviously are working on Sunday!