The Premise Behind Taking a Knee as a Way of Protesting Is Simple
It even exists in other mammals.
Kneeling is one of the most understandable and recognized positions a person can take. It is a simple position to enter into for the person kneeling and is easily identified by observers. It takes its cues from a core principle in mammalian nonverbal behavior: reducing the body's appearance shows respect, esteem, and deference. According to an article in Scientific American, kneeling "...is seen, for example, in dogs and chimps, who reduce their height to show submissiveness. Kneeling can also be a posture of mourning and sadness. It makes the one who kneels more vulnerable. In some situations, kneeling can be seen as a request for protection." The act is so obviously polite that it has stood as a sign of respect for thousands of years. For example, Christianity cites it in numerous instances in the Bible. In Psalm 95:6 it states, "Come, let us worship and bow down, let us kneel before the Lord our Maker;" in Chronicles 29:29, "Now at the completion of the burnt offerings, the king and all who were present with him bowed down and worshiped," and in Mark 10:17, "As He was setting out on a journey, a man ran up to Him and knelt before Him, and asked Him, “Good Teacher, what shall I do to inherit eternal life?" to name a few.