This summary is not the rule. The rule text controls.
Lawyers have to be honest when they're dealing with people outside their own client, like opposing parties, witnesses, or other lawyers. This rule says a lawyer can't knowingly lie about an important fact or a point of law while working on a client's case.
The rule also covers situations where staying silent would be just as bad as lying. If a lawyer knows their client is committing fraud or a crime, and speaking up is the only way to stop the lawyer from helping that wrongdoing, the lawyer generally needs to say something. The one exception is if another rule, 32:1.6, requires the lawyer to keep that information confidential. In that case, confidentiality wins out.
Basically, this rule keeps lawyers from lying to get an advantage for their client and stops them from using silence as a way to help a client cheat or break the law. It builds trust in the legal process by making sure people can rely on what a lawyer tells them, even when that lawyer represents someone else's interests.