What lawyers say isn’t “evidence.” (That’s unless they are testifying, which is quite rare.) Evidence comes only from witness statements; it consists of testimony and the exhibits that lawyers admit through that testimony. So, lawyers’ opening statements, objections, and closing arguments don't comprise evidence.
Without supporting evidence, juries aren’t allowed to accept as fact something a lawyer says. For example, if a lawyer interrupts a witness’s testimony by yelling, “He’s got the date wrong,” the jury must disregard the comment. Only some other kind of evidence—say, another witness giving the accurate date—can constitute proof that the witness did, in fact, get the date wrong.
When lawyers make improper comments, judges frequently remind the jury that the statements of attorneys are not evidence. In one federal case, for example, the appellate court found improper the prosecutor’s remark that the defense’s argument would be the “standard” argument by defendants facing drug charges. But the court found the prosecutor’s argument otherwise appropriate and convincing, and that the judge cured the misconduct in part by advising the jury that the lawyers’ arguments weren’t evidence. (United States v. Clark, 535 F.3d 571 (7th Cir. 2008).)