信念

All his convictions deserted him. / He lost faith in everything.

political conviction

steadfast faith

unshakable faith

strengthen one's belief; increase one's faith

form a conviction

lack conviction/faith

abandon/give up one's belief

hold to one's conviction; adhere/cling to one's faith; uphold one's belief

concrete one's conviction

deepen one's conviction/faith

cherish a conviction

forsake/renounce a faith

shake sb's conviction/belief/assurance (in)

hold a belief

retain one's faith