Let's analyse the verse step by step:
وَإِذْ أَخَذَ اللَّهُ مِيثَـقَ النَّبِيِّيْنَ لَمَآ ءَاتَيْتُكُم مِّن كِتَـبٍ وَحِكْمَةٍ ثُمَّ جَآءَكُمْ رَسُولٌ مُّصَدِّقٌ لِّمَا مَعَكُمْ لَتُؤْمِنُنَّ بِهِ وَلَتَنصُرُنَّهُ قَالَ ءَأَقْرَرْتُمْ وَأَخَذْتُمْ عَلَى ذلِكُمْ إِصْرِى قَالُواْ أَقْرَرْنَا قَالَ فَاشْهَدُواْ وَأَنَاْ مَعَكُمْ مِّنَ الشَّـهِدِينَ
And [recall, O People of the Scripture], when Allah took the covenant of the prophets, [saying], "Whatever I give you of the Scripture and wisdom and then there comes to you a messenger confirming what is with you, you [must] believe in him and support him." [ Allah ] said, "Have you acknowledged and taken upon that My commitment?" They said, "We have acknowledged it." He said, "Then bear witness, and I am with you among the witnesses."
(3:81 -SAHIH INTERNATIONAL Translation)
And (remember) when Allah took the Covenant of the Prophets, saying: "Take whatever I gave you from the Book and Hikmah (understanding of the Laws of Allah, etc.), and afterwards there will come to you a Messenger (Muhammad SAW) confirming what is with you; you must, then, believe in him and help him." Allah said: "Do you agree (to it) and will you take up My Covenant (which I conclude with you)?" They said: "We agree." He said: "Then bear witness; and I am with you among the witnesses (for this)."
(3:81 -MUHSIN KHAN Translation)
This verse says Allah has taken a covenant of the prophets ()!
Prophets unlike Messengers actually don't have the duty to spread Allah's message, even if they may get revelation (wahy), their duty is to live according to the message at hands and apply it in their daily life and (only) teach it when asked -so they don't need to be actively preaching!
Messengers in contrast must preach the message that's their mission and some of them have been given a (new) scripture (else why would we talk about Zabur (Psalms?), sohof -papers- Ibrahim and Musa, the Torah and Injeel beside the Qur'an and why would the Qur'an quote some of them in the same verse).
What is the covenant Allah took?
Let's read and make some conclusion from the above text:
SAHIH INTERNATIONAL translation says:
"Whatever I give you of the Scripture
MUHSIN KHAN translation says:
"Take whatever I gave you from the Book"
- A prophet () has been given "a scripture" (parts of it) not "the scripture" (the whole), so he has knowledge of parts of the message of Allah for example tawheed! But not all of it.
- Note that that both translations here may lead to a somewhat inaccurate meaning as scripture or book are meant generally not a specific book so saying the book or the scripture actually doesn't go along with the Arabic original (see my explanation on Arabic terms later)!
SAHIH INTERNATIONAL translation says:
and wisdom and
MUHSIN KHAN translation says:
and Hikmah (understanding of the Laws of Allah, etc.), and
- Beside knowledge of the scripture prophets have been given wisdom (or Arabic hikmah which comes from hukm: how to decide, give a verdict etc.): this might mean how to apply the scripture, and generally about rulings and how to apply them, about manners -as a part of the message- etc.
SAHIH INTERNATIONAL translation says:
then there comes to you a messenger confirming what is with you,
MUHSIN KHAN translation says:
afterwards there will come to you a Messenger (Muhammad SAW) confirming what is with you
- now if a prophet or many prophets was/were alive and a messenger came (according to SAHIH INTERNATIONAL translation which is more close to the truth as it doesn't exclude other messengers, while MUHSIN KHAN say it is only Muhammad () which certainly applies, but is too restricted). And if this messenger was confirming the message they have got, or in what they have from the scripture or wisdom.
Note here are many "if"'s all these are conditions or criteria that must be fulfilled simultaneously.
SAHIH INTERNATIONAL translation says:
you [must] believe in him and support him."
MUHSIN KHAN translation says:
you must, then, believe in him and help him."
- this actually is an essential part of covenant if all the above conditions apply the prophets () are asked to follow (believe) and help (support) the messenger.
- Note that Arabic here uses strong words of to emphasize the necessity to follow and support by adding an invocation to each verb meaning they must support and must follow no matter what.
- Now let's assume their came a false "Messenger" with a false message (going against the scripture or at least not confirming it at all, for example allowing zina) would the prophets need to follow him? No as this men is preaching something which goes against what the prophet had in his scripture.
- Or let's assume prophet x lived 60 years and died without meeting or hearing from any new messenger who came with a new revelation or a message confirming his message and preaching Allahs message would this prophet have fulfilled the covenant? Yes, even if he didn't need to as during his life no new messenger was sent with a message.
The MUHSIN KHAN translation practically applies to all prophets as none of them met Muhammad () as far as we have been told and taught. While the SAHIH INTERNATIONAL translation has some examples in the qur'an for example the prophet Yahya () was alive when 'Isa has brought a "new message" (the injeel) and he supported 'Isa.
'Isa in the Qur'an when addressing bani Isara'il says:
And [I have come] confirming what was before me of the Torah and to make lawful for you some of what was forbidden to you. And I have come to you with a sign from your Lord, so fear Allah and obey me. (3:50)
so 'Isa is an example of a messenger who came after a whole lot of messengers and prophets and who confirms their teaching, but brought some ease -in the religion- with him (by making lawful what was forbidden before his "new message"). The same may apply to Ibrahim () and Lut () and Ya'qub and Yousuf etc.
SAHIH INTERNATIONAL translation says:
[ Allah ] said, "Have you acknowledged and taken upon that My commitment?"
MUHSIN KHAN translation says:
Allah said: "Do you agree (to it) and will you take up My Covenant (which I conclude with you)?"
- This verse is the part that covers the acknowledgement and confirmation of the covenant. Allah who inspired his prophets () by revelation also asked them to confirm that they would support a messenger that actually fulfils the given criteria or conditions.
And in the next part of the verse the Qur'an shows their agreement or affirmation:
SAHIH INTERNATIONAL translation says:
They said, "We have acknowledged it."
MUHSIN KHAN translation says:
They said: "We agree."
Before quoting the final and important words that Allah is witness of this covenant which means He expects from each prophet () to fulfil his duty if the conditions are met:
SAHIH INTERNATIONAL translation says:
He said, "Then bear witness, and I am with you among the witnesses."
MUHSIN KHAN translation says:
He said: "Then bear witness; and I am with you among the witnesses (for this)."
As seen nowhere the verse says that Muhammad or any Messenger had to meet the prophets () or did take the covenant or even need to travel between time and space or whatever. It says that Allah asked every prophet () to stand by side by side with any messenger that they might meet while they are alive if and only if this messenger first confirms what they have in hand of the scripture and wisdom and secondly has been given the order to spread the message. This doesn't need any Angels, as humans can do this task easily.
Also note that the Qur'an uses the words:
- كِتَـبٍ "Kitabin" a book or a scripture or a message (in generally not exclusively) instead of الكتاب "al-Kitab" meaning the book, the message or the scripture (exclusively).
- حِكْمَةٍ "Hikamatin" a wisdom (also as a plural and in general without exclusion) instead of الحِكْمَة "al-Hikmah" the wisdom (exclusively).
- رَسُولٌ "Rassulun" referring to a messenger (generally not exclusively) not الرَسُولُ "Ar-Rassulu" referring to one special messenger (exclusively)
Note that this verse on the whole is addressing the people of the scripture: those people who have heard or have been reached by some of the precedent messages. So they also know about this covenant according to the Qur'an and that's what many scholars say: Not only the prophets have to follow a messenger also his followers should follow and support him if the conditions or criteria are met.
See also What is the meaning of Meethaaq taken from the prophets (Anbiaa)? (Meetaq is Arabic for covenant)
Finally the Qur'an quotes a couple of messengers -mostly by name- (note that all messengers were prophets, as, as explained being a messenger means being a prophet with an extra duty) they might not be more than 30 some ahadith quoted amounts of prophets and amounts of messengers some are more others less reliable. But what is certain is that the amount of messengers is lower than that of prophets. And Allah knows best!