7. How is Muhammad a mercy and a universal Messenger to all His creations when he demised more than 1400 years ago? The answer to this is like taking a peep into the future of mankind to which our Prophet Muhammad (pbuh) (during his time) was not a privy to and this explained why he was desolated when many were still unbeliever despite his intensive missionary work.
If their spurning is hard on thy mind, yet if thou wert able to seek a tunnel in the ground or a ladder to the skies and bring them a Sign, (what good?). If it were Allah’s Will, He could gather them together unto true guidance: so be not thou amongst those who are swayed by ignorance (and impatience)! 
If they turn back, thy duty is to convey the Message; and in Allah’s sight are (all) His servants.
We made thee not one to watch over their doings, nor art thou set over them to dispose of their affairs.
(Muhammad) Say: “I have no power over any good or harm to myself except as Allah willeth. If I had knowledge of the unseen, I should have multiplied all good, and no evil should have touched me: I am but a warner, and a bringer of glad tidings to those who have faith.” 
Thus if we examine the above verses clearly we will note that whereas Prophet Muhammad (pbuh) was clearly sad over a period, Allah, on the other hand, is clearly making reference to a bigger picture in the future. Similarly, mankind today does not see the bigger picture as such many disrespect God and became ungrateful.
Say: None in the heavens or on earth, except Allah, knows what is hidden. 
With Him are the keys of the Unseen, the treasures that none knoweth but He. 
Truly Man is, to his Lord, ungrateful; and to that (fact) he bears witness (by his deeds).
For Allah carries out all that He wills.
Notwithstanding Prophet Muhammad (pbuh) is not a privy to the Divine Plan but through him God sent His mercy and that is:
- God gave a name to the existing monotheistic religion as “Islam” as well as perfected and accepted it. He also decreed that Islam is the only universal religion (accepted by Him) and as such this is a foregone conclusion. He advised that one must not die except in the religion of Islam.
- God sent down the Holy Quran for all His creations and to date He protected the authenticity of the Holy Quran. With the authenticity of Quran protected, so too the faith of His believers.
- From the Holy Quran evolved apart from As Sunnah (Prophet’s Traditions), the Islamic Law (Syariah). Punishment under Syariah involves, in cases of Hudud: amputation, stoning to death, whipping and others. In cases of Qisas, it involves the principal of “an eye for an eye”. These strict laws are unpalatable to the Western people. But truly (Revelation) is a cause of sorrow for the Unbelievers. But verily it is Truth of assured certainty. So glorify the name of thy Lord Most High. To every People have We appointed rites and ceremonies which they must follow, let them not then dispute with thee on the matter, but do thou invite (them) to thy Lord: for thou art assuredly on the Right Way. The woman and the man guilty of adultery or fornication flog each of them with a hundred stripes: let not compassion move you in their case, in a matter prescribed by Allah, if ye believe in Allah and the Last Day: and let a party of the Believers witness their punishment.
And those who launch a charge against chaste women, and produce not four witnesses, (to support their allegations), flog them with eighty stripes; and reject their evidence ever after: for such men are wicked transgressors; Unless they repent thereafter and mend (their conduct): for Allah is Oft-Forgiving, Most Merci
The punishment of those who wage war against Allah and His Messenger, and strive with might and main for mischief through the land is: execution, or crucifixion, or the cutting off of hands and feet from opposite sides, or exile from the land: that is their disgrace in this world, and a heavy punishment is theirs in the Hereafter. As to the thief, male or female, cut off his or her hands: a punishment by way of example, from Allah, for their crime: and Allah is Exalted in Power. Full of Wisdom. We ordained therein for them: “Life for life, eye for eye, nose for nose, ear for ear, tooth for tooth, and wounds equal for equal.” But if anyone remits the retaliation by way of charity, it is an act of atonement for himself. And if any fail to judge by (the light of) what Allah hath revealed, they are (no better than) wrong-doers.  If any do fail to judge by (the light of) what Allah hath revealed, they are (no better than) Unbelievers.
The religion before Allah is Islam
This day have I perfected your religion for you, completed My favour upon you, and have chosen for you Islam as your religion.
If anyone desires a religion other than Islam (submission to Allah), never will it be accepted of him; and in the Hereafter he will be in the ranks of those who have lost (all spiritual good). 
O ye who believe! fear Allah as He should be feared, and die not except in a state of Islam.
This day have those who reject Faith given up all hope of your religion: yet fear them not but fear Me.
And this is a Book which We have revealed as a blessing: so follow it and be righteous, that ye may receive mercy
“This is no less than a Message to (all) the Worlds and ye shall certainly know the truth of it (all) after a while.”
Verily this is no less than a Message to (all) the Worlds.
We have, without doubt, sent down the Message; and We will assuredly guard it (from corruption).
Say: “If the whole of mankind and Jinns were to gather together to produce the like of this Quran they could not produce the like thereof, even if they backed up each other with help and support.”
Upon the demise of our Prophet Muhammad (pbuh), the mercy from Allah he left us are:
- The perfected religion of Islam.
- The Holy Quran (including As Sunnah).
- The Islamic Law or Syariah.
With the demise of our Prophet Muhammad (pbuh), the responsibility of bringing the wayward to fold fell upon our shoulders.
O ye that believe! betray not the trust of Allah and the Messenger
Those who faithfully observe their trusts and their covenants.
Our tasks are twofold namely:
- To equip ourselves fully for the task.
- To bring the Lawless rebels to fold.
A. To equip ourselves fully for the task
At every moment, God teaches us that which we have no knowledge. This He does for mankind but not for Iblis and his cronies. Hence we should spend every moment of our life learning the knowledge sent to us by God so as to equip ourselves for an ever bigger task to come.
And He taught Adam the names of all things; then He placed them before the Angels, and said: “Tell Me the names of these if ye are right.” They said: “Glory to Thee: of knowledge we have none, save what Thou hast taught us: in truth it is Thou Who art perfect in knowledge and wisdom.” He said: “O Adam! Tell them their names.” When he had told them, Allah said: “Did I not tell you that I know the secrets of heavens and earth, and I know what ye reveal and what ye conceal?” 
And if all the trees on earth were pens and the Ocean (were ink), with seven Oceans behind it to add to its (supply), yet would not the Words of Allah be exhausted (in the writing): for Allah is Exalted in power, full of Wisdom.
Say: “If the ocean were ink (wherewith to write out) the words of my Lord. Sooner would the ocean be exhausted than would the words of my Lord, even if we added another ocean like it, for its aid.”
Read! and thy Lord is Most Bountiful, He Who taught (the use of) the Pen, Taught man that which he knew not.
He has created man: He has taught him speech (and Intelligence).
Men who celebrate the praises of Allah, standing, sitting, and lying down on their sides, and contemplate the (wonders of) creation in the heavens and the earth, (with the thought): “Our Lord! not for naught hast thou created (all) this! Glory to Thee! Give us salvation from the Penalty of the Fire.
 An An’aam (6):35
 Ali Imran (3):20
 An An’aam (6):107
 Al Araaf (7):188.
 An Naml (27):65; Al Maidah (5):109; 116; Al Jin (72):26.
 Al Anaam (6):59.
 Al Aadiyaat (100):6-7
 Al Hajj (22):18
 Ali Imran (3):19
 Al Maidah (5):3
 Ali Imran (3):85.
 Ali Imran (3):102
 Al Maidah (5):3
 Al An’aam (6):155
 Shad (38):87-88
 At Takwir (81):27; Al Qalam (68):52
 Al Hijr (15):9
 Al Israa (17):18
 Al Haqqah (69):50-52
 Hajj (22):67
 An Nur (24):2
 An Nur (24):3-4
 Al Maidah (5):33
 Al Maidah (5):38
 Al Maidah (5):45
 Al Maidah (5):44
 Al Anfaal (8):27
 Al Mukminun (23):8
 Al Baqarah (2):31-34
 Luqman (31):27
 Al Kahfi (18):109
 Al Alaq (96):3-5
 Ar Rahman (55):3-4
 Ali Imran (3):191