And whatsoever ye do, do it heartily, as to the Lord, and not unto men. Paul is writing this, in context, largely to slaves — people whose work was compulsory, unpaid, and performed for masters who had no claim on their respect. If the principle holds there, it holds anywhere.
He is not saying the work is fine or that the master deserves it. He is relocating the audience. The question stops being is this person worth my best and becomes who am I actually working for. That reframing is the only thing that makes excellence possible in a job nobody notices.
Heartily translates a phrase meaning from the soul. It is the opposite of the half-attention most of us bring to repetitive work — the meeting we attend while thinking about something else, the task done to the standard of not being complained about.
This cuts both ways and both are useful. It dignifies work that feels beneath you, because the Lord is the one receiving it. And it convicts work you have been coasting through because no one is checking. Ye serve the Lord Christ — which means there is no such thing as an unobserved job, and no such thing as a job too small to be an offering.