Deeds that seemed unimportant at the time would prove to have been momentous; a tiny act of selfishness and unkindness or, conversely, an unconsidered act of generosity would become the measure of a human life.
And sometimes it's the very otherness of a stranger, someone who doesn't belong to our ethnic or ideological or religious group, an otherness that can repel us initially, but which can jerk us out of our habitual selfishness, and give us intonations of that sacred otherness, which is God.