Belief in the Prophets and Messengers is one of the pillars of faith, not belief in the Messengers only
Question

In the lengthy hadith of Jibreel, when he asked the Prophet (blessings and peace of Allah be upon him) about faith, the Prophet (blessings and peace of Allah be upon him) mentioned the pillars of faith, which include belief in the Messengers. As is well known, not every Prophet was a Messenger, so does this mean that it is not essential to believe in those who were Prophets but were not Messengers?
Praise be to Allah.The belief that is required is belief in both the Messengers and the Prophets, not only in the Messengers. This is one of the givens of the faith. The pillars of belief are explained in the Holy Quran.
Allah, may He be exalted, says (interpretation of the meaning):
“Say, [O believers], ‘We have believed in Allah and what has been revealed to us and what has been revealed to Abraham and Ishmael and Isaac and Jacob and the Descendants and what was given to Moses and Jesus and what was given to the prophets from their Lord. We make no distinction between any of them, and we are Muslims [in submission] to Him”
[al-Baqarah 2:136]
“Righteousness is not that you turn your faces toward the east or the west, but [true] righteousness is [in] one who believes in Allah , the Last Day, the angels, the Book, and the prophets and gives wealth, in spite of love for it, to relatives, orphans, the needy, the traveler, those who ask [for help], and for freeing slaves; [and who] establishes prayer and gives zakah; [those who] fulfill their promise when they promise; and [those who] are patient in poverty and hardship and during battle. Those are the ones who have been true, and it is those who are the righteous”
[al-Baarah 2:177].
Think about how Allah enjoined upon the believers belief in all of the Messengers and Prophets, of whom He named Ismaa‘eel (Ishmael), Ishaaq (Isaac) and the Asbaat (translated above as the Descendents), and told us that the believers do not make any distinction between any of the Prophets and Messengers; rather they believe that anyone who denies the Prophethood of one whose Prophethood was affirmed by Allah is a disbeliever, because disbelief in one of the Messengers or Prophets is disbelief in all the Messengers.
Al-Qaadi ‘Iyaad (may Allah have mercy on him) said:
The ruling on the one who reviles any of the Prophets of Allah, may He be exalted, or belittles them, or rejects the message they brought, or denies them, or disbelieves in them, is the ruling of our Prophet (blessings and peace of Allah be upon him). End quote.
Ash-Shifaa (2/1097).
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
The Muslims believe in all the Prophets and make no distinction between any of them. Belief in all the Prophets is obligatory; whoever disbelieves in one of them has disbelieved in all of them, and whoever reviles any of the Prophets is a disbeliever, according to scholarly consensus. End quote.
As-Safadiyyah (2/311)
Al-‘Allaamah as-Sa‘di (may Allah have mercy on him) said in his commentary on the verse quoted above from Soorat al-Baqarah:
From this we may understand that we should believe in all the Books that were sent down to all the Prophets, as well as in the Prophets in general and those whose names are mentioned in this verse in particular, because of their honourable position and because of the laws that they bought. What is required with regard to belief in the Prophets and Books is that we should believe in them in general terms, and with regard to those about whom more details are given, we must believe in them in detail.
Tayseer al-Kareem ar-Rahmaan (p. 67)
With regard to the famous hadith of Jibreel which was narrated by Imam Muslim (no. 8) from ‘Umar ibn al-Khattaab (may Allah be pleased with him), it says in it: He said: Tell me about faith (eemaan). He said: “It is to believe in Allah, His angels, His Books, His Messengers, the Last Day, and to believe in al-qadar (the divine will and decree), both good and bad.”
What is meant here is not to restrict it to believing in the Messengers to the exclusion of the Prophets; rather the word “Messengers” here includes the Prophets too. The reason why the word “Messengers” appears on its own is that they are more well-known, based on the verses quoted above, which indicates that it is obligatory to believe in all the Prophets.
Differentiation between the Prophets and Messengers does not apply in all cases; rather when one of the two words is mentioned in the text, what is meant is both the Prophets and Messengers. A distinction between them is only made when both words appear in a single text.
And Allah knows best.