To teach is to learn twice

अधिगत्य गुरोर्ज्ञानम्
छात्रेभ्यो वितरन्ति ये ।
विद्यावात्सल्यनिधयः
शिक्षका मम दैवतम् ॥

The teachers are those who master knowledge from their teachers and then impart it to students. They are the treasure houses of knowledge and love. I consider such teachers as divine beings and worship them.

(Some people excel in mastering the knowledge. Some people are skillful in imparting the knowledge. A teacher is the one who possesses both these qualities and hence is referred to as a treasure of knowledge)

To teach is to learn twice.