What is the ruling of Islamic law regarding a husband remaining with his wife or separating from her, after discovering her weak religiosity and ignorance of some basic religious matters, despite her positive answer when asked before the engagement?

The Prophet, peace and blessings be upon him, encouraged marriage to a religious woman. Religiosity is not limited to a specific type of worship or knowledge; rather, it is a collection of attributes and morals. A wife's ignorance of some matters of her religion does not preclude her from being described as religious. It is advisable to strive to teach the wife and help her obey Allah, by encouraging her to associate with righteous women, listen to lessons and sermons, and by using wisdom and gentleness, and seeking Allah's help.