Should a sin come to a person, he should think to himself that if they would decree upon him to convert he would willingly let himself be killed for Kiddush Hashem, so if he would let himself be killed - which is such a difficult test to withstand, how much more so should he not let himself sin in this far easier test!
And if one should have fantasies in middle of prayer, he should press his big toes into the ground strongly, and lean his whole weight upon them without holding on to the wall, and this will remove from him all types of fantasies...
... And should a sin present itself to a person, he should pray for Hashem to save him from it with all his heart; for on temporary suffering a person prays, so on eternal suffering which has no end and no measurement, how much more so should a person pray much!
And if one succeeds to overcome his urge and not sin, let him not give himself credit and say, "what a Tzadik I am, that I withstood this test", rather let him praise Hashem that he didn't sin, for all hearts are in Hashem's hands, as it says in Mishlei (21:1) "rivers of water, the heart of the king is in Hashem's hand, to wherever He desires he turns it", and it says in Bereishis (20:1), "and I have also withheld you from sinning to Me".
... And the Yetzer Hara is similar to an "itch". If one continuously scratches the itch, it will bring up scars, but if he holds back from scratching it will go away.
To see the full piece in Lashon Kodesh, click here.