First Thing the Comforter (Holy Spirit) Does

Nevertheless I tell you the truth; 

It is expedient for you that I go away: 

for if I go not away, the Comforter will not come unto you; 

but if I depart, I will send him unto you. 

And when he is come,  

he will reprove the world of sin, 

and of righteousness, 

and of judgment..

John 16:7,8