This phrase is very commonly used to refer to earning sufficient money to keep oneself alive.It means to just be able to pay for the things that you need in order to live i.e have money sufficient to pay for the necessities of life and not able to spend for luxurious things .
The idiom is derived from the Christian notion that life continues only as long as the soul inhabits the body.
1)He can barely keep body and soul together on what he earns.
2)We cant take his help, he himself is unable to keep his body and soul together.
3)He is striving for a job so that he can keep his body and soul together.
4)How will we keep our body and soul together with this earning and my husband's expenditure