You have asked me to answer your question. Is this because I do not come a religious background but I am a Christian by choice?
I am definitely not a Christian by natural birth. Nobody is. Although, you can be a Judahite by natural birth. You can be Islam by natural birth also.
Actually, you can be Roman Catholic by natural birth or Orthodox, Coptic or even claim membership of any of the Protestant religious institutions where baby baptism is practiced. These are merely cultural organizations that have a religious pretext, really. Just like being born into Christendom does not mean you are a Christian.
A person can be born into Christendom and be a secularist of some sort, maybe an atheist (does not believe the Creator exists), or an agnostic (accepts there is evidence for a Creator but is still uncertain as to what degree of influence regarding human affairs is attributable to Him), or a deist (believes in a Creator who has established principles both moral and physical for the Universe to function). None of these views acknowledge the Creator as worthy of devotion or that there is any need for a relationship with the Divine. Those who hold to these views see man as left to himself.
When you talk about seeking the opinions of those who have a non-Abrahamic background, I have a non-Abrahamic background in respect to where I was born and raised. Even though I have become a Christian, I am still an outsider looking into the cultures of the past. My acceptance of the Old and New Testaments are based upon the fact the reality of my experience is what these books point to happening if someone discovers the truth of existence.
Unbeknownst to me at the time of my search for the truth, the Bible instructs people to do what I did in order to encounter the Lord God. This instruction is found in the Old Testament as well as the New Testament.
The fact is that Jews who became Christians after the death and resurrection of Lord Jesus Christ taught from the Old Testament books and showed that He was the Messiah. Here is a case that was cited by the Gentile convert Luke:
Now a Jew named Apol′los, a native of Alexandria, came to Ephesus. He was an eloquent man, well versed in the scriptures. He had been instructed in the way of the Lord; and being fervent in spirit, he spoke and taught accurately the things concerning Jesus (Acts 18:24–25).
The Quran actually speaks about Jesus quite a bit. Saying that Jesus was born of a virgin and did not die but was taken to Heaven and shall return again (Quran4:157–158)—whereas Muhammad died.
But when it comes to Jesus, reading the New Testament would have to be the strongest argument. Although, some might say a stronger argument for the truth of the Gospels is the fact that the Quran declares Jesus was born of a virgin, He did not die and He is going to return again, and demonstrates His superiority to other religious figures.