In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Allaah (The Most High) informed us that the believer amongst the people of Pharaoh said:
يَـٰقَوۡمِ إِنَّمَا هَـٰذِهِ ٱلۡحَيَوٰةُ ٱلدُّنۡيَا مَتَـٰعٌ۬ وَإِنَّ ٱلۡأَخِرَةَ هِىَ دَارُ ٱلۡقَرَارِ
“O my people! Truly, this life of the world is nothing but a (quick passing) enjoyment, and verily, the Hereafter that is the home that will remain forever.” 
Mujaahid (rahimahullaah) narrated: Abdullaah Ibn Umar (radiyallaahu-anhumaa) said: Allaah’s Messenger (sallal-laahu-alayhi-wasallam) took hold of my shoulder and said: ‘’Be in this world as if you were a stranger or a traveller.’’ The subnarrator added: Ibn Umar Used to say: ‘’If you survive till the evening, do not expect ti be alive in the morning, and if you survive till the morning, do not expect to be alive in the evening, and take from your health for your sickness, and (take) from your life for your death.’’ 
The Muslim is like a stranger in this worldly life: The stranger is one residing in a country other than his country. The worldly life is not the Muslim’s permanent place of residence; rather the Muslim’s permanent place of residence is paradise. He is in this worldly life to work for entry into Paradise. He takes what is needed from this world to aid him work for entry into paradise.
The Muslim is like a traveller in this worldly life: The traveller takes rest during his journey and then carries on travelling. He does not reside permanently in that place he stopped to take a rest. In the life of this world the Muslim is that traveller. In reality he is not a permanent resident in the worldly life because his time in it is very little. His nights and days take him towards the afterlife.
What is befitting the Muslim with regards to the days, nights, and his health etc! If you reach the morning do not delay good deeds till in the evening because it maybe that you will not reach the evening. If you reach the evening do not delay good deeds till the morning because it maybe that you will not reach the morning. Do not delay repentance and righteous deeds till another time.
As long as a person is in a state of good health and wellbeing, he is able to perform fasting, the night prayer etc; but when he becomes sick he is not able to perform fasting, the night prayer etc. Therefore, as long as Allaah has given you good health, then hasten towards righteous actions because a time will come in which you will be unable to perform them-either due to illness, old age, or senility. Prepare for death and what is to come after it. Allaah gave you this life in order that you busy yourself with what will benefit you in the afterlife. So do not spend your life in play and jest. 
References: Soorah Ghaafir: Ayah 39; Bukhaari: The Book of Ar-Riqaaq Vol 8: Hadeeth Number: 6416];  Source: An Excerpt from ‘Al-Minhatur Rabbaaniyyah Fee sharh al-arba’een of Al-Allaamah Saaleh Al-Fawzaan (may Allaah preserve him) pages 285 287. slightly paraphrased]