Sentence:  But, my hearers, there are <WSD>Rubicons</WSD> to be passed in our religious and moral course, as well as in our temporal—occasions in the experience of our hearts, which extend their influence so far into the future, that it mainly depends on the decision we "then" make, and the purposes we "then" form, whether we shall at last be saved or lost for ever. 
Meaning of the word marked with <WSD> tags:  A limit that when surpassed cannot be returned from, or an action that when taken cannot be reversed.