What does Ezekiel 46:12 mean?

If the prince wants to give a voluntary offering—either a burnt offering or a peace offering—he should use the east gate to enter and leave, just like on the Sabbath. After he leaves, the gate should be closed again. Ezekiel 46:12 - Modern Text Bible

(This explains how the prince can bring extra offerings out of his own desire, and that the same entrance rules apply as on the Sabbath.)