The bread of life
There is a simple literal interpretation of this phrase, which is - the food that we require for physical sustenance. It is rarely used in that way though and is most often use figuratively to mean the spiritual food needed for a full life. It is specifically used in that way by the Christian church to refer to Jesus Christ.
From the Bible, John 6:35 (King James Version)
"And Jesus said unto them, I am the bread of life. He that cometh to me shall never hunger; and he that believeth on me shall never thirst."
Apart from the Bible, the earliest reference to the phrase in literature is by Philip Stubbes in his The anatomie of abuses, 1583:
"To breeke the bread of life to their charges."