I'm not a linguist, so this is just my opinion.
(どなたか別の方にもご回答頂けましたら幸いです。)
"は" has a function of "differentiation" or "contrast".
In your example, "本はあります" indicates that you don't have something else, which is "辞書".
EX) 私はスポーツを見るのは好きです。
So I understand that she/he likes to WATCH sports, but she/he probably does not like to PLAY sports.
EX) 私はスポーツを見るのが好きです。
This is just a self introduction, and she/he just like to watch sports and does not mean anything else.
I hope it helps :)