ב"ה, כ"ו שבט, תשט"ו
ברוקלין.
שלום וברכה!
... אף מי שעבר עבירה מימיו ושנקרא לו שם רשע פעם אחת בימי חייו יכול להיות בינוני - כן מוכח מתניא ר"פ י"ד שכל אדם כו' בכל עת ובכל שעה - ומש"כ ברפי"ב: ולא עבר כו' ולא יעבור לעולם - פי' שמצבו עתה כזה שלא עבר כו' (שאין כל רושם בנפש כו'). אף שדוחק קצת, ומוכרח גם ממרז"ל שתשובה מועלת לכל, ומוכרח גם מדוד המע"ה שחטא בשנים - כמרז"ל - ועליו נאמר צדיקים יצ"ט שופטן כו' (תניא פ"א).
B"H, 26 Shevat, 5715. Brooklyn.
Shalom u'Vrachah!
... Even someone who has committed a transgression in his life and was once called wicked at some point in his life can become a beinoni—this is proven from Tanya, beginning of chapter 14: every person etc. at any time and at any hour. And what is written in chapter 12: "and he has not transgressed etc. and will never transgress"—the meaning is that his current state is such that he has not transgressed etc. (that there remains no trace in the soul etc.). Even though this is somewhat forced, it is also necessary based on our sages' statement that teshuvah is effective for everything, and it is also necessary from David HaMelech who sinned in two matters—as our sages say—and about him it is said: "the righteous have their yetzer tov judge them etc." (Tanya ch. 1).
Summary
The Rebbe teaches that no matter one's past sins, through teshuvah one can reach the level of beinoni or even tzaddik. Tanya and the words of our sages show that spiritual transformation is always possible.