Einstein is endlessly enlisted as a secret believer. He wasn't. He spoke warmly of the 'God' of Spinoza — the lawful order of nature — but flatly rejected a personal God who hears prayer, and called himself an agnostic and a 'religious nonbeliever.' His line about God not playing dice was about physics, not devotion. It is only fair to say plainly: he did not become a Christian, or a theist.
See his 1954 letter to Eric Gutkind; linked reference below.
Sources & further reading