If the Law of Moses is still in force today, why don't we observe all Mosaic laws? Do we "pick and choose" which laws to keep and which not to keep?

First, our understanding of terms such as "the Law" and "Law of Moses" should be clarified. The expression "the Law" can mean the Torah, or Pentateuch, which consists of the first five books of the Bible. The same term (and the related phrase "Law of Moses") can also be defined as the regulatory system that defines the parameters of the Covenant God made with the nation of Israel. If we have the latter definition in mind, then "the Law" is essentially synonymous with "the Covenant." This was the law that was "added because of transgressions, till the Seed should come to whom the [Abrahamic] promise was made" (Galatians 3:19). It served as a "tutor [custodian—RSV] to bring us [Israelites, Jews] to Christ, that we might be justified by faith" (Galatians 3:24). Once Jews become true believers in the Messiah, they "are no longer under a tutor [custodian]" (verse 25).

When Jesus said, "Do not think that I came to destroy the Law or the Prophets…. Till heaven and earth pass away, one jot or one tittle will by no means pass from the law till all is fulfilled" (Matthew 5:17–18), He meant that the Law and the Prophets—the Holy Scriptures—would continue to be a valid source of divine revelation for as long as heaven and earth continued to exist. Jesus did not mean that every law of the Mosaic Covenant would remain in force indefinitely. That would make no sense since many of those laws never did apply to people outside the Covenant.

When Paul speaks of the Law as a "custodian" that was temporarily "added," he was speaking of the Law as a regulatory system. He was not saying that the Law (Torah) was no longer a good source of revelation and instruction for Christians.

The Mosaic Covenant contained many features that pertained exclusively to the people under the Covenant. But it also contained many universal features— laws, and commandments (moral precepts) that are always, and in every place, in effect. The Ten Commandments, for instance, while stated in terms significant to Israel's history and experience (see Exodus 20; Deuteronomy 5), represent ten universal moral categories. They were in full force long before the Mosaic Covenant was established, and they remain in full force today."

"Even the case laws of the Law of Moses are instructional in that each is founded on a universal moral principle. Therefore, to understand how or whether a particular law applies today, you must discern that law's purpose. Circumcision does not apply and never has applied to all men at all times, but (beginning in the time of Moses) only to men seeking membership in the Mosaic Covenant (or to the baby boys of people under that covenant). If there is no longer a Mosaic Covenant (cf. Hebrews 8:13), there is no need for circumcision. In that case, neither circumcision nor uncircumcision counts for anything (Galatians 5:6; 6:15). But the parapet and oxen laws have a different purpose (see Deuteronomy 22:8; 25:4). Those are situational regulations. They're not ceremonial laws; they're practical, and they have a moral dimension.

The parapet law was for people who used their rooftops for work and leisure. Failing to install a parapet could result in charge of criminal negligence if someone fell off the rooftop. Today, the tops of buildings are used for weddings, parties of various sorts, family or special group gatherings, and other events. Some have swimming pools, bars, and other such features. The building owner could be fined heavily for letting people use the top of his building if it didn't have a wall or fence to keep people from accidentally falling off. And if the owner allowed a group to party on the unsafe top of his building, and someone stumbled over the edge and fell to his death, the owner could face criminal negligence charges. The moral dimension of that law is that you should care about your neighbor enough to make sure he's safe when he's on your property. Here's another way of putting it: "You shall love your neighbor as yourself."

If you have an ox, you should feed him. If you work him by having him tread out the grain all day, you should feed him accordingly. This was not as much about the ox as it was about the owner of the ox. A cruel, self-serving man would hold back on feeding the ox; a kind, conscientious person would not. Such cruelty/neglect or kindness/care expressed toward a working animal would carry over to human relationships. This law tells us we should be kind and caring, not cruel and negligent.

The Law of Moses is chock full of universal moral principles and examples like those above. The moral dimension of the Law is such that Jesus could say, "Therefore, whatever you want men to do to you, do also to them, for this is [this sums up (NIV)] the Law and the Prophets" (Matthew 7:12)."