The main difference between the religions is in the time or their advent, for they taught to the needs and understandings of their times. Today, the needs of the planet are urgent, in particular for justice and unity, and thus the later Prophets have addressed more clearly that planetary need.
For example, the equality of men and women, the need for education (believe it or not, these are elements of Islam.) The Baha'i faith and Prophets as well as subsequent movements have added a great emphasis on non- violence, unity and the independent investigation of truth, matters which would have been above the understanding of previous generations. Baha'u'llah taught that all religions are one and no one Prophet is above another, although Their teachings do vary with the needs of the age.
Compassion today must embrace equality, justice, the oneness of humanity and the healing of the planet. That can only come, inevitably, through the spiritualization* of all humanity. When we are spiritual, we will more fully tap into our love and compassion for all humanity, rather than focusing on the selfish individual and material need.
If Compassion is the basis of all faiths, that again accentuates the principle that the "spiritualization* of all humanity is a key element for the healing of our time.
* Unity & the spiritualization* of all humanity are top goals for myself and the Baha'i community,
brought forth from our contemporary teachings and occupying our efforts as a group & in the world.