I've learned over the years that when " Grace" is remembered as the theological centre of Christianity it truly does become great, but sadly I have to admit it is not what Christian's are known for today or in the past, but it was what Jesus was known for and he always pointed to God as the architect of grace.
Not knowing the details of many religions, only generalities, I sincerely ask, does this concept exist within other "religions"?
Not that I have really come across. Most religions are works-based (Buddhism's eight-fold path, Hinduism's various paths of yoga, Islam's pillars, and so on).
Judaism is arguable. After all, in Judaism God essentially blesses a people and, even if God knocks them around a bit when go off the beaten path, in the end if you're a Jew, God will save/bless you and bring you back.
Of course, it can be argued as to whether Jesus himself believe in sola gratia. After all,
Matthew 25:31-46 (sheep and the goats) can certainly be read as saying people were being saved or punished based on what they did or did not do. Sola gratia may well be a creation of the Church, not Jesus, depending on how you read the Gospels so is arguably not inherent to the religion. Though it is a reading of Christianity that I, personally, find appealing. Admittedly, I lean universalist rather than Calvinist, but the principle that Grace is given rather than earned remains.
But I don't know that, while sola gratia is certainly one of the concepts that makes Christianity stand out, it make Christianity in any way superior to, say, Buddhism. It is not a view of the universe that coheres well with many people's experience of reality. Buddhism's Four Noble Truths (Life is suffering, Suffering comes from grasping/attachment, Suffering is relieved by ending grasping/attachment, Relieving grasping/attachment comes through the eight-fold path) describe a world somewhat more attuned to what I hear about and experience than unmerited grace does. Though the idea of Total Depravity, that we are mired in sin and that is what causes suffering, kind of lines up with the first two, Buddhism is quite clear that it our action that will change it, not a divine being.