All shabads of Siri Guru Nanak Dev jee in Raag Gauri are pretty hard to understand. They contain many mystical secrets and without Santhiya it's hard to do correct Pad-chhed and place proper Bishraams.
ਗਉੜੀ ਮਹਲਾ ੧ ॥
ਉਲਟਿਓ ਕਮਲੁ ਬ੍ਰਹਮੁ ਬੀਚਾਰਿ ॥ ਅੰਮ੍ਰਿਤ ਧਾਰ ਗਗਨਿ ਦਸ ਦੁਆਰਿ ॥ ਤ੍ਰਿਭਵਣੁ ਬੇਧਿਆ ਆਪਿ ਮੁਰਾਰਿ ॥1॥Guru Sahib here is talking about the Naabh Kamal which has turned at 180 degrees when Bichaar (Simran) of Brahm Vaheguru jee was done. When the Kamal faced upwards, then the flow of Amrit from Dasam Duaar began and then the Jyoti Saroop Muraari Vaheguru was seen piercing the whole world.
ਰੇ ਮਨ ਮੇਰੇ ਭਰਮੁ ਨ ਕੀਜੈ ॥
ਮਨਿ ਮਾਨਿਐ ਅੰਮ੍ਰਿਤ ਰਸੁ ਪੀਜੈ ॥੧॥ ਰਹਾਉ ॥Here in the Rahao Pankiti, Siri Guru jee is giving Updesh to the mind to not do Bharam (doubt, Dubidha) and when one accepts from heart i.e. Mann karki Mann lave, then one can drink Amrit Rass.
The above is based on the understanding realized from reading books of Bhai Sahib Randhir Singh jee.
Gurbani is Agam Agaadh Bodh.
Kulbir Singh