But the questions they asked were of an ordinary, simple nature. People should be able to know these without questioning the Prophet. Hence, he himself draws their attention to something of importance and tells them of one grave sin, namely backbiting. This is a sin which people always commit. It is very easy to fall into the trap of backbiting.
People tend to make fun of others when they are absent.
When this happens and other people laugh, there is always the temptation to make further fun of the same person and that may lead to exaggeration, false claims and lies. That adds insult to injury. It is then a double offence which puts the person who commits it in a very difficult position. The Prophet expresses that difficulty by saying that person sends himself to perdition. That is a very wise method of teaching.