It is the people nature to forget things if they not forced to remember things, you can do something good today, tomorrow, one month, one year and then probably stop.
But when people choose a religion they will be forced to do always good things, because they know if they will be good they will go to paradise and if they are bad they will go to hell for some time and then heaven.
See reality Nic if parents do not send their children to school, will the children go to school?
Most probably no.
please go through this link to understand more
http://www.islamicity.com/Mosque/uiatm/un_islam.htm
Nic here is also a short article of one page on Islam and the aime of life
http://english.islamweb.net/ver2/archive/article.php?lang=E&id=134339