Grace, blessings, and charity can come from the most unlikely sources and individuals. This is the central premise of Chisa Hutchinson’s Surely Goodness and Mercy, in which a precocious 12-year-old boy and a cantankerous school lunch lady are a pair of unlikely saviors. Set in Newark, N.J., the play shows that amid the grit and grime of urban life, simple acts of benevolence can have reverberating and profound effects.