This summary is not the rule. The rule text controls.
Law clerks work closely with judges, helping them research cases and prepare for decisions. This rule says lawyers cannot try to sway a law clerk's opinion about a case that is still being decided by the judge that clerk works for.
The point is to keep the decision-making process fair. Judges are supposed to make up their own minds based on the law and facts presented in court, not because someone pressured their staff behind the scenes. If a lawyer tries to talk to a law clerk about the strengths or weaknesses of a pending case, hoping to sway the outcome, that lawyer is breaking this rule.
This protects everyone involved in a case. It means both sides can trust that the judge's decision comes from an honest look at the case, not from outside influence on the judge's staff.