the direct meaning of will power is the mental power. We should be able 2 control our desires or also known as Quwate Shahwiya. The will power is mportant in many ways one of them r that u can attain the pleasure of ALLAH, etc.
The world that we live in distracts us from our main goals, which r 2 worship ALLAH and please HIM in every way we can, this world rings us towards DRUGS, PORNOGHRAPHY, etc.
If a person has will power it means that he is keeping himself away of these bad habits such as sleeping late and behavior, etc. In the month of RAMADHAN it is a regular thing 2 fast but it is not a regular thing 2 try and close down a large number of bad things which we usually do.
Once the PROPHET (S) was asked, don’t you have a voice inside you(a Shaitan) which tells you to do evil? And HE replied, YES I DO! but i keep it locked up.The NAFS is not tied by chains of metal but with the WILL POWER. this shows how improtant it is.