Reason 1: We all come from a common root.
Christianity and Islam, despite their general claims to exclusivity, both emerge from the Jewish faith. Jesus was not a Christian, and Abraham was not a Jew. The traditions we tend to hold as absolute always have roots that precede the traditions.
Actually, all religion stems from earlier practices that have changed via the process of “civilising”, by agricultural, industrial, technical and cultural progress.
And less obvious is that mankind has emerged from a very much longer tradition – the natural evolution of Earth, itself part of an even more immense cosmic drama over billions of years.
It would be great if we were awed and humbled by this, accepting that “We are the universe made conscious of itself” as Thomas Berry observed. But many religious people hold stubbornly to stories which keep them inside small boxes, driven by pride and fear.
Any progress always requires us to gain fresh insights into our roots. Bede Griffiths tells us that the religions are like the fingers. To the quick observer, they appear as separate. But as we deepen we find they are all part of the hand.
There is a path of deepening in every tradition. In Christianity it might be called the contemplative, in the Jewish traditions, the Kabbalah, and in Islam, Sufism. If one studies these mystical traditions, their similarities become clear. But if we insist on adhering to the outer, obvious orthodoxies, we will get caught up surface differences.
We must never forget our root. Remembering will allow us to move forwards.