Very beautiful Bhai Sahib jee. I am delighted to read this. The link that you provided had the following lines written by Alaama Iqbal:
ਹਮ ਦੁਆ ਲਿਖਤੇ ਰਹੇ, ਵੋਹ ਦਗ਼ਾ ਪੜ੍ਹਤੇ ਰਹੇ। ਏਕ ਨੁਕਤੇ ਨੇ ਹਮੇਂ, ਮਹਿਰਮ ਸੇ ਮੁਜਰਿਮ ਬਨਾ ਦੀਆ।(I kept writing Dua (prayer) but they read it as dagha (deception). Due to the difference of one dot, the Mehram became Mujrim).
Between Dua and Dagha there is a difference of only one dot and same way there is only difference of dot between Mujrim and Mehram. Basically he is saying that his friend misunderstood his intentions.
Bhai Gurdas jee is stating a deeper thought:
ਇਕਤੁ ਨੁਕਤੈ ਹੋਇ ਜਾਇ ਮਹਰਮੁ ਮੁਜਰਮੁ ਖੈਰ ਖੁਆਰੀ ।It seems that Bhai Sahib is stating that one small mistake can turn a friend into an offender. One mistake can spoil the spiritual life of a Gursikh. A Sikh may be doing a lot of bhagti but one deviation from rehit can spoil it all. One spark of fire can burn tonnes of cotton. One drop of lemon juice can spoil the whole pot of milk. Sometimes, one small mistake or sin can spoil the whole life worth of spiritual earnings. We must be careful in what we do and say. We should always stay submitted to Guru Sahib.
Kulbir Singh