Impure thoughts become sin when we entertain them. Everybody has impure thoughts of one type or another. That’s part of being human. Having an impure thought come into your mind is not a sin by itself; choosing to entertain the thought is a sin.
It is very appropriate for the Golden Gate or the Eastern Gate to be linked to the Pure Gate. This gate will be opened when the Pure and Holy One comes. The Messiah has already entered the predecessor of this gate once before riding on a donkey a few days before He died to pay for our sins.