Thad was made to hurt Barry Allen by killing his daughter Nora West Allen and push The Flash to his breaking point.  To force Barry to do the unthinkable to kill Thaddeus or put in a state that make him wish for death. 

To taut the man after committing the act and tell him about Nora's involvment with him and that Thad was her son. That Barry killed his own grandson.  Only Eobard knew what was supposed to happen every step of the way. 

A way to totally  destroy  Barry emotionally,  and morally.   To ruin the family after forcing himself upon it. 

That is Thad's purpose.  That is what his 'father' wanted, nothing more.  But Thad had no idea about the whole plan