At the start of the year, we need to keep in mind that one more year of our lives has gone. If our actions were evil, and we were treading the path to Jahannam, we have now come one year closer to it. And if we were in search of Jannah then we now have one year less to reach that goal. In brief, the end of the year means the end of a year of our lives. An Arabic poet says,

The passing of days please a person,
But this passing(in reality) is the passing of his life.

We need to always value each and every second of our lives, as we may not live to see the 1st of Muharram next year; in fact we may not live to see the next moment. This is what Imam Bukhārī rahimahullāh highlighted in the following couplets,

Value the reward of Salāh whilst you have the time to do so,
For it is possible that your death is sudden.
I have seen many healthy people without any form of illness
Whose healthy soul departed suddenly