"Do not judge, or you too will be judged." Matt 7:1
This sounds simple enough. But does this interpretation make sense? We actually want to be judged, or how do we go to be with God? We also want to be judged correctly by others. We like receiving credit where credit is due, for starters.
So obviously this would be better interpreted to say that we shouldn't judge with a condemning heart, so that we won't be judged by a condemning heart.
Amidst this it could also be looked at to say that if we judge others with a condemning and unforgiving heart, that we will judge and condemn ourselves by the same standard: We won't really accept in our hearts that Christ's atonement can cleanse a person who has made errors (which includes ourselves).
As Christ stated _
"...Forgive, and it shall be forgiven you" Luke 6:37 or "Forgive us our debts as we also have forgiven our debtors." Matt 6:12
We will notice that others have done evil to us or others. Recognising that others have done evil isn't a bad thing. How can we avoid doing evil ourselves if we don't know recognise evil? But Christ is saying to forgive.
Christ warns, "but beware of men..." (Matt 10:16) [Some women may echo that]. But in all seriousness, he is saying to be wary of people in our dealings with them. This requires judgement.
We also have to find a marriage partner. While revelation as to whom to marry is advised, there is still a need for us to understand the person and whether they are suitable - judgement. The same applies if we have children. How can we help them to learn and in their squabbles if we don't judge them?
And what of bishops and stake presidents etc in dealing with confessions or accusations of serious offences.
So how do we judge righteous judgement?
Isaiah says in regard to Christ _
"...he shall not judge after the sight of his eyes, neither reprove after the hearing of his ears." Isa 11:3
We have the tendency to judge people by their actions and words. Yet he is saying this isn't fair judgement. This then requires us to learn to judge by the intent of their heart and the perception in their mind. It is impossible to judge such a way without either an ability to see inside others or to use the Holy Ghost or both.
Moroni states the following _
"For look, my brethren, it is given to you to judge, that you may know good from evil... so, I show to you the way to judge; for every thing which invites to do good, and to persuade to believe in Christ, is sent forward by the power and gift of Christ; so you may know with a perfect knowledge it is of God." Mor 7:15-16
So Moroni is telling us how to judge. He's gone on in verse 17 to declare that those who subject themselves to the devil can be determined by the criteria of judgement he has set forth. Obviously, therefore, he hasn't regarded Christ's statement as posing that we don't judge people.
Either way I wish to stress again that the Holy Ghost is best used in any judgement we make. And if our judgement is made with a view to helping others move on from mistakes, we will accept our mistakes with the same attitude.