Preserve your conscience always soft and sensitive. If but one sin force its way into that tender part of the soul and dwell there, the road is paved for a thousand iniquities.
And take heed that under any scruple, doubt or temptation whatsoever, you never let any reasonings satisfy your conscience, which will not be a sufficient answer or apology to the great Judge at the last day.
From his juvenilia Advices to a young man