To survive. The phrase is most often used specifically to refer to earning sufficient money to keep oneself alive.

The phrase derives from the Christian notion that life continues only as long as the soul inhabits the body. Walter Ralegh, the English explorer and courtier, expressed that view in his 1608 poem - The Lie, in which he describes the soul as "the body's guest".

Later in the 17th century Richard Crashaw wrote, in his poem Temperance (1652),:

And when life's sweet fable ends,
Soul and body part like friends;
No quarrels, murmurs, no delay;
A kiss, a sigh, and so away.