In some way, regarding compassionate wisdom, the secrecy can also be a bit explained by this funny example/metaphor about meditation. I think it all starts from being aware for own mind protection.
"...But as Shantideva said, it's not something impossible, you can do it. It's like drinking
alcohol. If you have never drunk alcohol in the past, then what do you have to do? If
you want to become a person who drinks alcohol, then what do you have to do? You
have to find the right master, someone who goes to the pub every now and then and
you have to hang around with him or her, then this person will give you the
transmission. In the beginning some of that alcohol might burn your throat. But that
is necessary if you want to be a diligent follower; you have to go through this
tolerance. If your master is very compassionate and skilful he might not give you a
whole bottle of alcohol at once because that will put you off. Then you will never
touch it again. But if he is skilful he will give you maybe one or two sips every day.
Then six months later, maybe you can drink half a glass. About a year later you will
speak every language in the bar....
....... " http://multimedia.getresponse.com/725/6 ... s/6834.pdf