From Longman Dictionary of Contemporary Englishmanna from heavenmanna from heavenGETsomething very good that you get when you did not expect to, just when you really need it → manna
Examples from the Corpus
manna from heaven• The letters are manna from heaven, filling my time and recharging my batteries.• The activities of illegal immigrant vessels were as manna from heaven to the media who naturally gave them much publicity.• The hijab is manna from heaven for politicians facing crises. 