It's a Chabad custom to read tehillim daily, and one of the chapters a person typically reads is their age + 1. So, for me, that's Chapter 34. A few days ago, in the Hayom Yom, a daily snippet of chassidus, it mentioned a passage from Gemara, and I had a thought.
In the Talmud, in Nidah 30b, it says that before a child is born, they are made to swear an oath, "be a tzadik and not a rasha." The acceptance of this oath is a condition for life. Incidentally, this passage (which goes on) forms a main discussion in the Tanya.
However, in Tehillim, Ch. 34, King David writes:
"Who is the man who desires long life...? Guard your tongue from evil and your lips from speaking deceit. Keep away from evil and do good."
In Nidah, it says "be a tzadik", in other words, do good, and then "not a rasha", don't do bad. But in Tehillim, the order appears reversed, "keep away from evil", and then "do good".
It would seem that to enter the world (birth), one must take an oath to do good, and also not to do bad. Yet, to stay in the world (long life), one must not do bad, and also do good.
How to explain this?
An unborn child is completely innocent - a tzadik. So the oath the unborn child takes is, I will continue to be a tzadik, and won't do bad things.
King David is not talking to a tzadik, but to a human being who has fallen and who knows this; who is afraid their life will be cut short in retribution for their deeds. What are they to do? So he tells them: You want to keep living? Stop your nonsense, and then do something good with the life you're given.