The Law is more concerned with why we do what we do than simply with what we do.
Consider the giving of an offering. Is this a good thing - is it good to give to the Church? Well... why did you give it. If it is an offering of love for the good of others and the support of the preaching of God's Word, yes, it is a good thing. If by giving to the Church you are hoping to acquire fame and glory for yourself - you have received your reward (i.e. it ain't a good thing). If you give because you feel guilty and the gift is an attempt to lessen your guilt - again, not a good thing. It becomes an idolatrous gift.
Why is important.
Likewise - is it a bad thing to kill? We even have the commandment - thou shall not kill. Well, why do you kill? Are you killing because you are angry and annoyed with someone who is cruel to you? Not good. Are you a soldier who is exercising lawful orders for the defense of others? That is something else entirely.
What doesn't tell you the story - why does.
This is because it is not what goes into the Body that defiles it, but what comes out of the heart. It is not enough to say "This is good, that is bad - follow this and you will do right" - why is important.
Is it good to observe the Sabbath? Sure. But it is good to pull your son out of a well, even on the Sabbath. And simply kicking up your feet, "resting" with NFL pregame stuff in the morning is not "rescuing your son". And, if you observe the Sabbath, not because you know you are a sinner in need of God, but rather because you are a good person who follows the Law - it is in fact self-centered wickedness of the highest sort.
We cannot simply say "This is good, that is not" - we must consider why something is done. Otherwise we will become hypocrites who think we worship God with our works while our hearts are far from Him.