Wa alaikum assalam sister,
Thank you for your kind words.
You kindly share "The 'Mu'min' I thought would be the one who believes in the angels, messengers, books etc."
Response:
Yes indeed, but only in the time context of the specific era that is being discussed.
For example, a 'mu'min at the time of prophet Solomon's ministry would be required to believe in the books that had been revealed up to that point and all the messengers that had preceded them and including Solomon himself.
Furthermore, the term 'Mu'min' is specifically linked to true faith which enters deep into the hearts of mankind placing belief in these aspects of faith. Therefore, in the context of prophet Muhammad's ministry, this would entail whatever would have preceded it, i.e. belief in 'all' the scriptures that went before it, the angels, God's messengers up to and including Prophet Muhammad etc.
Similarly, in the time of Prophet Abraham and his context, this deep seated belief would be dependent on his particular time context and what had preceded him. This is also true of prophet Moses and his people.
Thus, from the time context of Prophet Muhammad's ministry, a believer is expected to hold the beliefs of their time era covering the eras that went before them. That is why I shared a premise sharing: 'In the context of the Quran and the Prophetic ministry..."
"In the context of the Quran and the Prophetic ministry, a 'Mu'min' was one that 'believed' in the veracity of the Quran and the messenger (i.e. Prophet Muhammad) (pbuh) that God appointed to deliver the final scripture to mankind. Therefore, a Mu'min believed in God, all His scriptures and His messengers."
For a Christian or a Jew today, for them to become 'believers' from a Quran's perspective, they would need to believe in the veracity of prophet Muhammad's ministry and the Quran as a guidance sent by God, whilst upholding the tenets of their own scriptures.
I trust that clarifies dear sister, God willing.
Your brother in faith,
Joseph