Back then I didn't think about the job deeply enough to start.
I never thought about work seriously then. That job, I just somewhat started it.
At that time I just started the job without thinking deeply about it.
当時は then, back then, at that time,
I didn't think about the job deeply
その仕事について深く考えていなかった
I never thought about work seriously.
仕事について真剣に考えなかった。
without thinking deeply about it
それについて深く考えずに
なんとなく、なぜだか somewhat, somehow