Gateway to knowledge or gateway for knowledge which is correct
According to me both the door of knowledge or the gateway of knowledge are right in their respective places. That which is generated by thinking through the mind and intellect is knowledge itself. Through the mind one can go to the door of knowledge and through the intellect one can enter knowledge. When the mind and intellect are activated, the thinking gets enhanced. All these are the means of knowledge. The door of knowledge or the gateway of knowledge are both absolutely right in their place. When the mind becomes elevated, the importance of the gateway of knowledge increases, which is related to the intellect.