We all know the story of Chanuka. The Yevanim went and contaminated all the oils in the Beis Hamikdash, but, the Kohanim found one small jug of pure oil that was Tahor, and it lasted 8 days. The Pnei Yehoshua asks, that we have a rule that if there is no choice one may do the Avoda in the Beis Hamikdash with contaminated oil too. If so what was the big miracle?
However, we must add another point. The Torah rules that gentiles do not contaminate at all. It is the Chachamim that added a stringency that Gentiles contaminate a severe Tumah which cannot be allowed in any circumstances.
Mattisyahu was particular to follow all the rulings of the Chachamim and therefore would only use the pure oil, and this rectified the sin of his father's misconduct not following the ruling of the Chachamim.
The Gemarah writes that a child with his good deeds can save and merit his father.
Therefore we say in Al Hanissim, in the days of Mattisyahu the son of Yochanan, to mention the fact that he rectified and saved his father.
