I wasn’t exactly sure what “probation” truly meant, so I looked it up in the 1828 dictionary:

Probation
PROBA’TION, noun [Latin probatio.] The act of proving; proof.

1. Trial; examination; any proceeding designed to ascertain truth; in universities, the examination of a student, as to his qualifications for a degree.

2. In a monastic sense, trial or the year of novitiate, which a person must pass in a convent, to prove his virtue and his ability to bear the severities of the rule.

3. Moral trial; the state of man in the present life, in which he has the opportunity of proving his character and being qualified for a happier state.

Probation will end with the present life.

4. In America, the trial of a clergyman’s qualifications as a minister of the gospel, preparatory to his settlement. We say, a man is preaching on probation

5. In general, trial for proof, or satisfactory evidence, or the time of trial.

It seems that the Number 3 definition would apply to Mrs. Eddy’s lesson title, “Probation After Death”–as she is challenging this notion that “Probation will end with the present life.”