The Christian Institute is asking the Government for assurance that it will never again force churches to close.
The organisation said it was a "colossal mistake" to close churches during England's second national lockdown.
Boris Johnson on Monday announced a return to tiered restrictions after the lockdown ends on December 2, with places of worship once again allowed to open their buildings for public worship.
Paragraph 72 of the new Covid-19 Winter Plan says: "The Government also recognises the significant sacrifices that people of all faiths have made this year; restrictions have been in place over a number of religious celebrations and observances, and it is thanks to these sacrifices that it has been possible to control the virus.
"Communal worship will be possible for all faiths in all three tiers and faith leaders continue to play a key role, consulting on how to make religious practice as safe as possible."
Christian Institute director Colin Hart said he was "delighted and relieved" that churches were being allowed to re-open but said the announcement was "long overdue".
"What we need now is an assurance that the Government will never shut churches again," he said.
"Patrick Vallance and Chris Whitty admitted the Government did not have good evidence to justify the forced closure of churches.
"In the second lockdown ministers seemed to believe that opening gardening centres was 'worth the risk' but opening churches was not.
"This sent a very damaging signal about their view of the place of the Christian faith in our national life. Public worship has not been suspended since before Magna Carta. Since then, through plagues and the Blitz, churches have remained resolutely open."
The ban on public worship was widely condemned by Christians, including leaders of the Church of England and Roman Catholic Church, and some 1,500 church ministers who signed an open letter challenging the restrictions.
Mr Hart said it was wrong of the Government to focus on protecting people's health and financial wellbeing while neglecting spiritual welfare.
"We recognise the huge pressure the Government has been under with the Covid pandemic, but their actions have focussed on meeting people's health and economic needs," he said.
"Vitally important though these are, people are not merely material beings. As Jesus said, 'man does not live by bread alone'.
"Many have been experiencing fear and isolation. But spiritual needs have been sidelined. Churches have been closed at the very time they needed to be open. Shutting them was a colossal mistake and one that must never be repeated."