Look, there are rules about comma placement that make a lot of sense. They are modern American rules; don't get confused with U.K. punctuation, which is slightly different. There were also fewer guidelines in the 19th century. Commas do not go after coordinating conjunctions (for, and, nor, but, or, yet or so) which connect two independent clauses. You should put a comma after therefore, but if it follows an independent clause, then it should likewise be preceded by a comma.