Allah says in Surah 2, Ayah 208.... "enter completely into the true religion".
One of the proposed interpretations is that this was revealed concerning some from Ahlul Kitaab who couldn't forgo their old habit of dignifying the day of Saturday. In response, Allah says to leave all that behind and to fully submit to all of the dictates of Islam.
This is a call to all of us to try and let our old bad habits die hard. May Allah make it easy... Ameen.