弁解 and 説明: defending oneself and explaining content
Compare excuses listing reasons for failure with an explanation of machine use. Explanations can serve a defensive purpose, and excuses are not defined as universally false.
Defending one’s actions
弁解 (べんかい) means an excuse or defense. 「彼は失敗の理由を並べて弁解した。」 says he made excuses by listing reasons for his failure.
「証拠を示され、もう弁解の余地はなかった。」 says the evidence left no room for further excuses. That situation does not define the nature of every excuse.
Making content or a method understood
説明 (せつめい) means explanation. 「先生が機械の使い方を分かりやすく説明した。」 says the teacher explained how to use the machine in understandable terms.
「詳しい説明は資料の二頁に載っています。」 places a detailed explanation on page two of the materials. An explanation can be written as well as spoken.
Reading purpose as well as content
When reasons for failure serve to defend the speaker, they can be presented as 弁解. An explanation intended to make content understood can also serve a defensive purpose.
Do not divide the terms into always false excuses and always true explanations. They concern purpose and function; the truth of a particular account requires separate evidence.
What purpose is assigned to the listed reasons in 「彼は失敗の理由を並べて弁解した。」?
Show the answer and why
They are presented as excuses defending him. Listing reasons does not turn them into a neutral explanation of a procedure, or establish that every reason is false.