There are questions and sometimes confusion about what laws written in the Old Testament for the Jewish people are to be followed by Christians today. The simplest way to answer that is simply THIS:  

If we are CLEARLY commanded in the NEW TESTAMENT Bible to do something, God expects us to obey the command.

That makes good common sense, doesn't it?

However - there are issues in the New Testament that God wants born again Christians seriously praying about and showing a willingness to be obedient to the leading of the Holy Spirit if they want to walk in increased wisdom. The subject of fasting would be one of those issues, for instance. Nowhere in the New Testament are Christians commanded to fast, but that doesn't negate the fact that there is GREAT wisdom in fasting when the Holy Spirit is prompting a person to fast. The subject of giving money to help advance the Kingdom of God in the lives of others is another one of those issues. Nowhere in the New Testament are Christians commanded to give money to the work of the Lord, but the Holy Spirit is more than eager to help Christians come to the realization that the law of sowing and reaping as never been nullified (which greatly has to do with both temporal and more importantly, eternal rewards).

Keep something in mind. Regarding the New Testament: It helps greatly in mentally separating what happened BEFORE Jesus went to the cross ... and then AFTER He resurrected. The New Covenant commandments OFFICIALLY took effect immediately after Jesus resurrected from the grave (though that doesn't negate ignoring what Jesus said prior to His resurrection -- wisdom always needs to be applied).

Keep something else in mind. God's moral laws have been in effect from the time of Adam and Eve, and will remain in effect as long as the human race exists. Don't confuse God's moral laws with Old Covenant - New Covenant commandments. Learn to understand WHO they were given to, and WHY (i.e., Old Covenant Jewish ceremonial laws; Old Covenant Jewish civil laws, Old Covenant Jewish food [health] laws).  

God instituted STRICT laws for the Jewish people prior to Jesus resurrecting from the grave to reveal to both Gentiles and Jews that the Jews had to pay a HUGE SACRIFICIAL PRICE to expect God's blessings or lose God's blessings. And aside from the Jews having been shown how important pure sacrificial blood was important to God that would one day point to the shed blood of God Himself (Jesus Christ) on the cross ... God always wanted to persuade ALL people -- Jews and Gentiles -- that it was IMPOSSIBLE for anyone to obey all the Old Covenant commandments to the Jews ... though Jesus Christ DID!

We must be very cautious and wise in how we interpret the following scripture passage: When Jesus said, "Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them." (Matthew 5:17) ... keep at least a couple of things in mind. Jesus made this statement before the cross. What that fully means will be debated until Jesus returns to earth again, but I believe God wants us understanding that Jesus was speaking of The 10 Commandments "Laws". The 10 Commandants (Laws) given in Exodus Chapter 20 are MORAL laws. It only makes sense that MORAL laws are STILL to be obeyed as best as we can obey them, but just like ALL the commandments in the New Testament given to Christians ... we ALL fall short of obeying every one of them all the time. (If we somehow COULD obey all of them, which we can't, God the Father wouldn't have needed to send mankind a Savior, would have He?)  

Christians are NOT saved from punishment for their sins by trying to obey those 10 moral Commandments ... but Christians ARE empowered by the Holy Spirit and expected by the Holy Spirit to do their very best to keep trying to obey them if we consider ourselves WISE. All New Testament commandments wisely understood and wisely applied are to be obeyed as well if we consider ourselves even WISER. Nevertheless -  We are NEVER saved from the penalty for our sins by obeying ANY laws (but we WILL be rewarded for diligently keeping them!). We ARE saved from the penalty for our sins and declared "NOT GUILTY!" on the Judgment Day by TRUSTING that what Jesus Christ accomplished for us on the cross is what saves us. How thankful (and WISE) we are for what Jesus Christ accomplished for us by lovingly taking our punishment on the cross when He didn't have to ... will clearly be discerned and seen by others in how we conduct our lives in accordance with New Testament Truth and our willingness to daily strive to walk by the (Holy) Spirit.

Satan wants believers perpetually confused on these matters briefly discussed here.  Confusion in these important matters helps rob believers of joy and peace with God and others.

Thus Satan delights in keeping Christians confused about matters of Old Covenant (testament) commandments given to the Jewish people, and New Covenant (testament) commandments give to ALL people - Jews and non-Jews - and he has no shortage of "Christians" to work on his behalf. Most of the New Testament Book of Galatians addresses this very issue. 

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Remember:  All that we do in this life comes back to our God-given purpose which is to serve and glorify God. The money and assets we accumulate, the fame and power we've attained or seek to attain - all of the things of this nature will one day pass away, but those lives of others we impact for Jesus Christ will last for eternity, and we will be rewarded for the part we helped play by impacting those lives ... for eternity. (Matthew 6:19-20 is our assurance)