Mohammed Mokhtar Gomaa said the decision should ensure that sermons during Islam's holy month of fasting "unite people, not divide them," compared to what he described as a more politicised past when the country was run by an Islamist president.
"The religious speech was politically driven, which affected the moral side," he told reporters at a news conference on the first day of the observance. "Now we're in a race against time trying to restore morals."
The measure is the latest attempt by the state to control religious speech following last year's overthrow of President Mohammed Morsi.
In recent months Egypt has banned Morsi's Muslim Brotherhood, which it declared a terrorist organisation, and passed a new law restricting protests.
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The ministry had already restricted preaching in mosques to state-authorised clerics.
In a separate development, a Cairo appeal court has set July 22 as the date of a retrial for a prominent Egyptian activist sentenced to 15 years in prison in absentia for organising an unauthorised protest and assaulting a policeman.
The sentence was the toughest against any of the secular activists behind the 18-day uprising that ended the reign of longtime autocrat Hosni Mubarak in 2011.
It is also the first conviction of a prominent activist since former army chief Abdel-Fattah el-Sissi took office.