Most important of all, the ba'al teshuvah must learn ahavat Yisrael, the love of fellow-Jews, be they observant or not.
Like all love, ahavat Yisrael cannot be reserved for those without blemish.
In fact, such saintly Jews do exist, more than it is generally assumed; fortunate is the one who can find his way to them.
But love demands something far more difficult; to see the flaws and yet forgive.
A saint once explained the verse, "Hate not thy brother in thy heart," (Leviticus 19:17) to mean "Hate not thy brother, in that thy heart is bigger than his."
One who is ready for such love, who is willing to accept his fellow-Jews for all their weaknesses, often discovers more good in them than he would otherwise have noticed.
–Rabbi Adin Steinsaltz
From "The Observant Community," in Teshuvah by Rabbi Adin Steinsaltz