ועשית את כל מצותיו אשר אנכי מצוך היום (נצבים ל:ח)

A person once wanted to travel to a specific city by train but did not have enough money to purchase a ticket. He was missing just a few ‘groschen’ (small coins) to make up the cost of the train fare. Having no choice, he bought a train ticket with whatever money he possessed, arriving at a city one stop before his desired destination. 

Upon his arrival, he stepped out of the train and found himself in a foreign city, knowing no one was there.  He thought, ‘It is a shame that because of a few groschen, I could not reach my desired destination, and now I have to trod amongst strangers in a strange city… 

The Gaon Reb Itzel’a Blazer zt”l explained that the same applies to Mitzvahs.  A person can perform mitzvahs all his life, but when he arrives in the Bes Din Shel Ma’alah (Heavenly court), he might be short of one Mitzvah that could have outweighed his sins, losing him the coveted warrant to enter Gan Eden.  Therefore, a person should not push off any mitzvah opportunity that comes his way because it could be that this one mitzvah will be the deciding factor in bringing him to his final destination in Gan Eden.