Ramcharit Manas – Bala Kanda – 21
राम नाम मनिदीप धरु जीह देहरीं द्वार।
तुलसी भीतर बाहेरहुँ जौं चाहसि उजिआर॥
Raama Naama manideep dharu Jeeha dehareem dvaara
Tulsi bheetaru baahiraihu jaum chaahasi ujeeaaru
Meaning by Swami Purushotamanandaji Maharaj of Vasishta Guha, Himalayas, who is the disciple of Swami Brahmananda (the great disciple of Sri Ramakrishna Paramahamsa) in his Auto biography, The story of Divine compassion
A lamp placed on the door step of a room lights up both the outside and the inside. The door to the body is considered to be the mouth. If one places a jewelled lamp on this pedestal, both the outside of the body as well as the inside get light. This jewelled lamp is the Ramanama – go on chanting the Rama Nama – Then both outside and inside, everywhere, there will be the light of knowledge – yes indeed the luster of knowledge.