Answer: First judges need to have certain qualifications. If they do not meet these certain qualifications, they are not qualified to be a judge.
Secondly, the judges go through the Vior Dire Examination. To begin a jury trial, a panel of prospective jurors is summoned. This panel will include a number of persons from whom a jury will be selected to try the case. Alternate jurors may be chosen to take the place of jurors who become ill during the trial.
The panel members are sworn to answer questions about their qualifications to sit as jurors in the case. You will be asked to fill out a short questionnaire. This helps the parties learn about you and will reduce the amount of time you must spend in court answering questions in person. This questioning process is called the voir dire. This is an examination conducted by the judge and sometimes by counsel or both. A deliberately untruthful answer to any fair question could result in serious punishment for the person making it.
Lastly, the final stage is the Juror's Solemn Oath. After the Vior Dire Examination is complete and they have passed, the Judge swears to be truthful.
Hope this helps!