Parshat Hayyei Sarah
In 25:11 the passuk says and after Avraham died, "ויברך אלקים את יצחק בנו" - And Hashem blessed Yitzchak his son.
We already know Yitzchak is Avraham's son. It has told us this many times. Especially now that Avraham has died what is the need to say "his son"?
I think this tells us that Yitzchak continued the ways and methods of Avraham after Avraham's death. Yitzchak showed everybody by his actions that Avraham was the influence in his life. He lived in a way that honored his father.
I know a Rav who very often quotes his father. if you go to him to ask a shailoh, very frequently he begins his answer by saying, "My father would do this.." or "My father held that..". He quotes from his late father even though he is a talmid chacham in his own right. He is continuing the path of his father. He lives and gives honor to his father.
That is Yitzchak. By Yitzchak's life you could see he was the son of Avraham. Even after Avraham's death.