While we are reminded to " cleanse first that which is within the cup and platter, that the outside of them may be clean also", Matt 23:26, and directly on point, "whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart", Matt 5:8, there is a story that comes to us through Tradition of St. John Chrysostom's spirited discussion on those subjects with a group of young, zealous monks.
It seems the monks were adamant that those evil thoughts led to condemnation, while St. John's position was that, while those thoughts are indeed wrong, they were insufficient. When the discussion wound down, St. John ordered the monks to fast for several days ahead of a feast he was planning. The monks spent several days in fasting and prayer, and finally St. John invited them to the feast. As they stood around the table smelling the food in front of them, St. John invited a Bishop in to bless the food before they ate.
The Bishop went on with his blessing for nearly an hour. At the end of the blessing St. John dismissed the monks back to their cells. When they complained that they hadn't eaten and were starving after their fast, St. John said, "surely you have already eaten this food in your hearts, so there is no need for you to eat it again".