Verily, God is my Lord and Your Lord, so, worship Him alone, this is the straight path.
2) Death and Purpose of Life:
We will all leave this earth one day, but do we think about it at all. But the reality, as God says, everyone shall taste death.
كُلُّ نَفۡسٍ۬ ذَآٮِٕقَةُ ٱلۡمَوۡتِۗ وَإِنَّمَا تُوَفَّوۡنَ أُجُورَڪُمۡ يَوۡمَ ٱلۡقِيَـٰمَةِۖ فَمَن زُحۡزِحَ عَنِ ٱلنَّارِ وَأُدۡخِلَ ٱلۡجَنَّةَ فَقَدۡ فَازَۗ وَمَا ٱلۡحَيَوٰةُ ٱلدُّنۡيَآ إِلَّا مَتَـٰعُ ٱلۡغُرُورِ (١٨٥) سُوۡرَةُ آل عِمرَان
Everyone shall taste death. And only on the Day of Resurrection shall you be paid your rewards in full. And whoever is removed away from the Fire and admitted to Paradise, he indeed is successful. The life of this world is only the enjoyment of deception. (3.185) Surah Al-E-Imran
Day of Judgement: It is an absolute demand of justice that there be a Day of Judgement on which every soul is brought to account.
قُلۡ إِنَّ ٱلۡمَوۡتَ ٱلَّذِى تَفِرُّونَ مِنۡهُ فَإِنَّهُ ۥ مُلَـٰقِيڪُمۡۖ ثُمَّ تُرَدُّونَ إِلَىٰ عَـٰلِمِ ٱلۡغَيۡبِ وَٱلشَّهَـٰدَةِ فَيُنَبِّئُكُم بِمَا كُنتُمۡ تَعۡمَلُونَ (٨) سُوۡرَةُ الجُمُعَة
Say (to them): “Verily, the death from which you flee will surely meet you, then you will be sent back to (God), the All-Knower of the unseen and the seen, and He will tell you what you used to do.” (62.8) Surah Al-Jumua.
Purpose of life: God states, He created us with the purpose of worshipping Him alone and to test who is best in actions.
ٱلَّذِى خَلَقَ ٱلۡمَوۡتَ وَٱلۡحَيَوٰةَ لِيَبۡلُوَكُمۡ أَيُّكُمۡ أَحۡسَنُ عَمَلاً۬ۚ وَهُوَ ٱلۡعَزِيزُ ٱلۡغَفُورُ (٢) سُوۡرَةُ
Who has created death and life, that He may test you which of you is best in deed?  And He is the All-Mighty, the Oft-Forgiving; (67.2) Surah Al-Mulk
Preparation for Death: God states,
يَـٰٓأَيُّہَا ٱلَّذِينَ ءَامَنُواْ ٱتَّقُواْ ٱللَّهَ وَلۡتَنظُرۡ نَفۡسٌ۬ مَّا قَدَّمَتۡ لِغَدٍ۬ۖ وَٱتَّقُواْ ٱللَّهَۚ إِنَّ ٱللَّهَ خَبِيرُۢ بِمَا تَعۡمَلُونَ (١٨) سُوۡرَةُ الحَشر
O you who believe! Observe your duty to Allah. And let every soul look to that which it sends on before for the tomorrow. And observe your duty to Allah. Indeed! God is Aware of what you do. (59.18) Surah Al-Hashr
Desire to Go Back: God says in the Qur’an:
وَأَنفِقُواْ مِن مَّا رَزَقۡنَـٰكُم مِّن قَبۡلِ أَن يَأۡتِىَ أَحَدَكُمُ ٱلۡمَوۡتُ فَيَقُولَ رَبِّ لَوۡلَآ أَخَّرۡتَنِىٓ إِلَىٰٓ أَجَلٍ۬ قَرِيبٍ۬ فَأَصَّدَّقَ وَأَكُن مِّنَ ٱلصَّـٰلِحِينَ (١٠) سُوۡرَةُ المنَافِقون
And spend (in charity) of that with which We have provided you, before death comes to one of you and he says: “My Lord! If only You would give me respite for a little while, then I should give charity and be among the righteous. (10) Surah Al-Munafiqoon
God created us and made us responsible for our actions by granting us freedom of choices, and intelligence to know right and wrong. If there is no after life, in which to reward the doers of good and punish the evil doers, it would contradict the perfect justice of the Almighty Creator.
Dr. Emdad Khan