Matthew 5:20, ​Matthew 5:29-30, Matthew 6:14-15, Matthew 18:8-9, Mark 9:45-47, Mark 11:25-26, and Luke 6:37

​Matthew 5:20
  • For I say unto you, That except your righteousness shall exceed [the righteousness] of the scribes and Pharisees, ye shall in no case enter into the kingdom of heaven. (Matthew 5:20)
Through many examples Jesus explained how difficult keeping the law is, how impossibly high the standard is.

Matthew 5:29-30, Matthew 18:8-9, and Mark 9:45-47
  • And if thy right eye offend thee, pluck it out, and cast [it] from thee: for it is profitable for thee that one of thy members should perish, and not [that] thy whole body should be cast into hell. And if thy right hand offend thee, cut it off, and cast [it] from thee: for it is profitable for thee that one of thy members should perish, and not [that] thy whole body should be cast into hell. (Matthew 5:29-30)
  • Wherefore if thy hand or thy foot offend thee, cut them off, and cast [them] from thee: it is better for thee to enter into life halt or maimed, rather than having two hands or two feet to be cast into everlasting fire. And if thine eye offend thee, pluck it out, and cast [it] from thee: it is better for thee to enter into life with one eye, rather than having two eyes to be cast into hell fire. (Matthew 18:8-9)
  • And if thy foot offend thee, cut it off: it is better for thee to enter halt into life, than having two feet to be cast into hell, into the fire that never shall be quenched: Where their worm dieth not, and the fire is not quenched. And if thine eye offend thee, pluck it out: it is better for thee to enter into the kingdom of God with one eye, than having two eyes to be cast into hell fire: (Mark 9:45-47)
Here we see more examples of that, as He so graphically depicts what would need to be done for any of us to attempt to keep the law perfectly.  When people realize they can't do it, they turn to Jesus Christ in faith:
  • But the scripture hath concluded all under sin, that the promise by faith of Jesus Christ might be given to them that believe. But before faith came, we were kept under the law, shut up unto the faith which should afterwards be revealed. Wherefore the law was our schoolmaster [to bring us] unto Christ, that we might be justified by faith. (Galatians 3:22-24)

Yet more examples of a similar nature:
  • ¶ And a certain ruler asked him, saying, Good Master, what shall I do to inherit eternal life? And Jesus said unto him, Why callest thou me good? none [is] good, save one, [that is], God. Thou knowest the commandments, Do not commit adultery, Do not kill, Do not steal, Do not bear false witness, Honour thy father and thy mother. And he said, All these have I kept from my youth up. Now when Jesus heard these things, he said unto him, Yet lackest thou one thing: sell all that thou hast, and distribute unto the poor, and thou shalt have treasure in heaven: and come, follow me. (Luke 18:18-22)
  • And he said unto him, Why callest thou me good? [there is] none good but one, [that is], God: but if thou wilt enter into life, keep the commandments. (Matthew 19:17)
  • Ye have heard that it was said by them of old time, Thou shalt not kill; and whosoever shall kill shall be in danger of the judgment: But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool, shall be in danger of hell fire. (Matthew 5:21-22)
  • Ye have heard that it was said by them of old time, Thou shalt not commit adultery: But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart. (Matthew 5:27-28)

Matthew 6:14-15, Mark 11:25-26, and Luke 6:37
Another set of related scriptures, and these are to do with conditional forgiveness:
  • For if ye forgive men their trespasses, your heavenly Father will also forgive you: But if ye forgive not men their trespasses, neither will your Father forgive your trespasses. (Matthew 6:14-15)
  • And when ye stand praying, forgive, if ye have ought against any: that your Father also which is in heaven may forgive you your trespasses. But if ye do not forgive, neither will your Father which is in heaven forgive your trespasses. (Mark 11:25-26)
  • Judge not, and ye shall not be judged: condemn not, and ye shall not be condemned: forgive, and ye shall be forgiven: (Luke 6:37)
But this is again the standard of the law that Christ fulfilled for us and that's imputed to us when we believe the gospel.  We know this because God forgave us first:
  • And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ's sake hath forgiven you. (Ephesians 4:32)
  • Forbearing one another, and forgiving one another, if any man have a quarrel against any: even as Christ forgave you, so also [do] ye. (Colossians 3:13)
So in forgiving others, we're passing along the grace we've received.  I think these verses can also relate that:
  • Who comforteth us in all our tribulation, that we may be able to comfort them which are in any trouble, by the comfort wherewith we ourselves are comforted of God. For as the sufferings of Christ abound in us, so our consolation also aboundeth by Christ. (2 Corinthians 1:4-5)