A sadhu (holy man) is a missionary. Preaching is the fruit of his labour. However, one must first gain some depth before he can really preach. What does this mean? It means that first he must have faith! Preaching is highly dependent on this. Sraddha (faith) comes from sraddh, that which has been heard from a bona fide source, and dha, to fix in the heart. So a sadhu fixes the Absolute Truth in his heart and then makes the endeavour to preach.
So how is it that the mind goes into sense objects and that sense objects go into the mind? It is because of upadis, various designations e.g. birth, passport, education, parents, schools, etc. We think that we are the doer of things which are actually carried out by the three modes of material nature but a sadhuwithdraws from these things, from these upadis.
When one is free from all these upadis then one can fix their mind on the Supreme Lord. By hearing of Krsna, by making sacrifice for Krsna, by going to places where Krsna is worshipped, in these ways asadhu finds his wealth. And when Krsna consciousness awakens, the sadhu will find compassion
But how to be compassionate… is it by kind words? No, just kindness is not real compassion. Real compassion is only possible when we have something better then we can feel compassionate for the conditioned souls.
In the material world, things usually get easier when we have been doing it longer, for example cooking gets easier the more you practice it. But in spiritual life, for a sadhu it becomes more difficult as he has to do more and more than ever to attract Krsna as Krsna wants more and more from us.