People can ask a question - why do worship, if everything is predestined? If the fate of a person to be a believer or unbeliever is already solved, then why whorship, why do anything at all, if all is predetermined, whom I will be in the Hereafter? This, of course, whispers from the Shaytan.
Scholar Ibn Hajar al-Haytham said wonderful words - if a person is destined to die an unbeliever, infidel, and even then he has to use in the commission of good deeds. In the Hereafter person, even a kafir, will be judged and will be asked for two things: first - for not believing in Allah and His Messenger, peace be upon him, and the second - for every sin that he committed on earth. He will be punished for having committed something forbidden - for having consumed alcohol (if consumed) for eating pork or other forbidden food. Therefore, if a man will not commit sins in this life, will try to be righteous, the punishment will be less, even if he dies an unbeliever. Therefore, in this - in the commission of good deeds - there is a benefit even for the unbeliever. But for the believer, the more obvious benefits of worship. Therefore, it is without a doubt, whispers from the Shaytan, who is trying to turn us away from the worship of Almighty Allah and obedience to Him. This is the first.
The second point, none of us knows how he will die. None of us have been told that we will die a believer or non-believer. Therefore, in this Hikmat, the wisdom of God, that the future is hidden from us, otherwise people would relax. If each of us knew the date of his death, he began to worship only one year (or even a month or a week) until death, for a period of time, would reduce it to a minute, five minutes. All the rest of the time he would spend in carelessness. We do not know when we will die, and that the wisdom of Allah and His mercy, that we should be in constant tension, that the next time, every next breath could be the last. And what state we are in this state we will be accountable to Allah. This should give the believer cheerfulness in worship, knowing that at any moment we can leave this life.