In Matthew 5 and really all the Gospels, JESUS who is GOD became a man, and went under the law. And revealed to the Jews (and all of us) the real standard of the law.  For example the 10 commandments were really 613 laws brought into a more manageable 10 to make it easier. These laws say; in fact most of the world agrees with it and says "dont murder, don't defraud/steal, dont cheat on your spouse"  etc.. most everyone believes and would agree with that.  But JESUS comes and shows what murder or adultery really is.  (not what we thought, it much higher and harder really impossible).  Have you ever drove in your car and got so mad at another driver, you said /thought or did something out of anger? We all have - to GOD's standard, which is the only standard that is murder.  Lust is adultery...etc..  

HE (GOD) is the standard.

So JESUS had to come to show us that we've broken all the laws, we are all guilty, we all in our own strength (if you can call it that) are not good - no not one.  We've all sinned, we are all guilty and as James said "if you've broken one law you've broken them all"  James 2:10

We are law breakers.

So the law 's standard is HIGHER than we thought because many of us say in our own defense "I've never killed no-one" and we think to everyone and more importantly GOD that that is impressive, or that makes us a so called "good-person" but JESUS says even more "if anyone says "You fool " shall be guilty.  

Ever thought or said a bad word, or even "fool" to someone. Ouch, its getting hot in here!

JESUS sums up the entire chapter of Matthew 5:48  by ending  it by saying : "be perfect like your heavenly FATHER is perfect".

It is no wonder that the disciples asked at another time: "who can be saved then"? Mark 10:26

So the law is it good or bad? Well it increases sin. Because when a law is given you want to try (with human effort) to keep it but the more you try the more you fail and break it. that's why new years resolutions nor "dont walk on grass signs either". They don't work. Romans 5:20 says: "the law was brought in so that the trespass (sin) might increase."  INCREASE??? So I guess the law is bad then??

Paul argues the law (these commandments) are good (see Romans 7:12) because GOD is like that (HE doesn't cheat, lie, murder) for GOD is love. Love meaning to live for others, to sacrifice for others, to provide and give, to the least of them. "So then, the law is holy and the commandment is holy, righteous and good" Romans 7:12

And it shows me, I'm not good.

Okay so the law does a pretty good job and beating us up and showing us where we are actually at (which is a deplorable state, on our own).

We do not keep the commandments we on the other hand, have broken them all but it isn't really me but sin that lives in me. You see you had no choice to choose "sin over righteousness" "As it is, it is no longer I myself who do it but it is sin living in me. Romans 7:17

Its the same now of righteousness - you have it without asking for it (like sin) and you do good things that GOD prepares you in advance - you just (under the new covenant) want to do them or just do them (you get to do them).

Want righteousness and good to walk in?  - then continue to bask and recognize HIS love for you "I'm the one that JESUS loves". The more we rest/live in/enjoy/brag on HIS love for us the more we believe that and become that and do that.  The churchy have it back-wards (like so many things) they talk to JESUS about how much 'they love HIM' not realizing that we love because HE first loved us. HE is LOVE and the obvious source of it.

So why with all this law-stuff then? Here is the key verse that gives us the birds eye view. Remember all have sinned...: and now this is GODS master plan "For God has locked all people in the prison of their own disobedience so that he may have mercy on them all. Romans 11:32   Read it again "MERCY on us ALL"

He locked us all up (the entire world past/present/future) so that HE can have mercy on us all. Even the "bad" ones that you self-righteously judge as bad because they killed someone but you are good because you (in your own futile mind believe) never did that - thus (trying to) justify yourself before GOD - when HE has instead put you and me in the "sin camp" so that HE because of JESUS has mercy on us all (not who ask, not who are self-righteous) but all.