Angels are invisible beings created from light who carry out Allah's commands. To believe in Allah, His prophets, and His books, a person must also believe in the existence of angels. This is because Allah conveyed His divine commands to the prophets through angels, and the prophets then shared these commands with humanity.
Believing in divine revelation, prophethood, the afterlife, heaven, and hell is only possible by believing in angels. So, before believing in the prophets and the divine books sent to them, it is necessary to firmly believe in the existence of the angels who bring prophethood, revelation, and the books.
In this respect, believing in angels means "believing in prophets." Denying angels is considered denying prophethood. This is why belief in angels comes after belief in Allah [the most Exalted ] in the "articles of faith."
As indicated in the Qur'an, after believing in Allah, it is commanded to believe in His angels, then His books, and His prophets.
In Surah Al-Baqarah, it says: “The Messenger believed in what was revealed to him from his Lord, and so did the believers. All of them have believed in Allah and His angels and His books and His messengers, [saying], “We make no distinction between any of His messengers.” And they say, “We hear and we obey. [We seek] Your forgiveness, our Lord, and to You is the [final] destination.”
Our Prophet [sallallahu alayhi wa sallam] spoke with the angel of revelation, Jibril [sallallahu alayhi wa sallam]. When Jibril asked him, "What is faith?" the Messenger of Allah [sallallahu alayhi wa sallam] replied:
“Faith is to believe in Allah, His angels, His books, His prophets, and the Hereafter.”
Anyone who denies the existence of angels, which is firmly established by clear texts like this, is considered a disbeliever according to the Qur'an, Sunnah, and the consensus of the Muslim community. This is because Allah the Almighty says:
“Whoever disbelieves in Allah, His angels, His books, His messengers, and the Day of Judgment has certainly gone astray.” (Surah An-Nisa 136) 
Characteristics of Angels
Angels are created from light. In a hadith narrated by Hz. Aisha [radiyallahu anha], the Prophet [sallallahu alayhi wa sallam] said:
“Angels were created from light. Jinn were created from pure fire. And Adam was created from what was described to you (soil).”
Angels, being created from light and being spiritual, have a nature and reality unique to them, which prevents them from being visible to the human eye. This is because the human eye is not created in a way or with the capacity to see luminous, deep, and abstract beings like angels. However, since Allah has given this ability to the prophets, who are sent as guides with superior qualities, only they have been able to see angels in their true form or in a form Allah willed. The fact that angels are not visible to us is not because they do not exist or are completely invisible, but because we are not created with the ability to see them.
There are beings that are known to exist, proven through knowledge, and felt, but cannot be seen. For example, the existence of the mind is an undeniable reality. X-rays, radio waves, and the sun's ultraviolet rays are truly existing things, but they are not visible to the eye.
