This phrase comes from the Latin bona fides, “good faith.” Bona fide is in the ablative case, which conveys “in/with good faith.” Mr. Gotobed undertakes to pay some legal fees for Goarly if Mr. Bearside can promise that the affair will be conducted “bona fide.” Mr. Bearside seals the transaction with a repetition of the Latin phrase–a verbal handshake, as it were, with its Latinity functioning as a kind of guarantee. Despite such assurances, there is not good faith on both sides, and Bearside and Gotobed eventually fall out in a disagreement about compensation. [KS & RR 2012]
I don’t understand your laws, but justice is the same everywhere
Mr. Gotobed is expressing his frustration over various customs and conventions in Britain. This is a problem throughout the text for Mr. Gotobed, as he believes in the supremacy of natural law and natural justice over conventional laws and societally specific ideas of justice. We can find discussion of the relationship between natural law and civil law in many ancient authors; the citation of Justinian below is a particularly concise example. [KS & RR 2012]
Source: Justinian, Institutiones 1.2.