The meaning behind this is that first and foremost it is only through wisdom and analyzation that a person can see the difference between good and evil.
Second of all, if a person has a thought, for example a desire for money, they can elevate the source of this desire which is love, into the love of God – and therefore when you elevate something to its source – the negative aspect falls away… the same thing can be about lust.
It is well-known that anything that a man despises, that causes that element to fall off.
Now it sometimes happens that a righteous person is feeling low, and when we are feeling low we don’t appreciate our own value – and because we don’t appreciate our own value, we don’t appreciate the value of our prayers and our Divine service – and that’s why Tzaddikim would often boast… because it would cause them to have a greater self-esteem.
This is why we find that the sages praised Rabbi Shimoin Bar Yochai very greatly… because he was the greatest Tzaddik, he had to descend very low, to elevate all the low thoughts and speech of men – and therefore the sages praising him, gave him a greater self-confidence, which allowed him to elevate himself.