Komentarz do Rodzaju 26:11

מות יומת, will be executed. The repetition of the word מות refers to death by human tribunal as well as by heavenly forces. The reason Avimelech used the word "whoever touches," was to warn his subjects that even conduct for which Gentiles normally are not punishable by death would become capital offences in this instance (compare what we have written on Genesis 20,4).

ויצו, after Avimelech had found out that Rivkah was Yitzchok’s wife, he had to inform the people of this fact to ensure that no one would touch her. Also, he had to warn the people not to harm Yitzchok, so that he would not be killed on account of his wife.