SuttaCentral
A line in the Metta Sutta says ‘not busy with duties’…
What exactly does this teaching entail?
On a first glance, with an untrained mind, it seems as if the Buddha encouraged us to be lazy or to avoid taking more (job) responsibilities.
Please help explain how ‘in actuality’ one can practice this teaching and is a responsible and caring member of one’s community (including but not limited to one’s family, friendly circle and dhamma community).
Thank you.
Dheerayupa
Hi, I think it means you need some spaciousness in life, so you actually have time for your family and your practice. If life is too filled with stuff (too much upadana), too much work, too much hobbies, too much desires, too much duties etc., then people are stressed out and it leads to a lot of aversion and dukkha. Personally I find much more plesant and paradoxically succesful people who do less things but have more space in life. Why? Probably because then you have more fun with less amount of things you’re doing. And because you’re generally well rested - you put more heart and energy into things. Also - for example when our family or kalyana-mittas have some problems, we actually have space to help them. If we’re too filled with stuff, there is no space for anything but stress.
So I think it is not about laziness, but about middle way between doing something worthwhile (right livelyhood) and having space for “more importaint things” like caring about others and ourselves, and to practice some meditation, and listen to dhamma… and like Ajahn Brahm says - to at least from time to time do absolutely nothing 
With Metta 
There are a few Suttas (search for “relish work”) that put work in one line with laziness and too much sleep:
AN6.14:3.1: Take a mendicant who relishes work, talk, sleep, company, closeness, and proliferation. They love these things and like to relish them.
AN6.14:3.2: A mendicant who lives life like this does not have a good death.
AN6.14:3.3: This is called
AN6.14:3.4: a mendicant who enjoys identity, who hasn’t given up identity to rightly make an end of suffering.
It almost looks like “work” is something that opposes the practice of the noble eightfold path.
Here, too, doing work is listed together with behavior that is considered inappropriate for monastics. It’s about the drawbacks of staying too long in the same monastery:
AN5.223:1.3: You have a lot of stuff and store it up. You have a lot of medicine and store it up. You have a lot of duties and responsibilities, and become capable in whatever needs to be done. You mix closely with laypeople and renunciates, socializing inappropriately like a layperson. And when you leave that monastery, you miss it.
In other places, being skilled in many duties is praised:
AN5.86:1.1: “A senior mendicant with five qualities is dear and beloved to their spiritual companions, respected and admired.
AN5.86:1.2: What five?
AN5.86:1.3: They have attained the textual analysis of meaning, text, terminology, and eloquence.
AN5.86:1.4: And they are skilled and tireless in a diverse spectrum of duties for their spiritual companions, understanding how to go about things in order to complete and organize the work.
AN5.86:1.5: A senior mendicant with these five qualities is dear and beloved to their spiritual companions, respected and admired.”
Maybe note that “being skilled in many duties” is not the only quality of that mendicant.
Probably, as @Invo has already pointed out, it’s all about balance; and, most importantly, not forgetting or neglecting other aspects of the path that take you to a deeper level, namely understanding the texts (as in our Sutta) and the calm of meditation.
IMO “unburdened by duties” or "Doesn’t takes duties as burden"can be closer translation. My reasons are as below
I would add to the good answers provided by other members is that busy-ness in this context should not be interpreted as the opposite of idleness, but the opposite of boredom and other unwholesome mental states.
I sometimes think of ‘not busy/unburdened with duties’ as not getting so emeshed in busy-ness that I forget to be mindful or to cultivate metta.
Early Buddhists believed the heart was the material basis for the mind, not knowing the function of the brain, and so not including it in the thirty one parts of the body.
“37. Dwelling in the cave (of the heart), the mind, without form, wanders far and alone. Those who subdue this mind are liberated from the bonds of Mara.”—-Dhammapada
Althought we now know the brain is the material basis for mind, recent scientific research finds that the heart has to a degree a share with the brain in the location of mind.
The research confirms the Theravada practice of metta and compassion as purely mental exercises to be soundly based and productive to others.
It could be that being beloved is a drawback 
There are not many examples in the suttas where the Buddha actually directs metta, however there are numerous cases of him referring to the “foolish, uninstructed ordinary person.” Therefore if used indiscriminately metta can be misdirected to the detriment of wisdom. The sense of separation that arises in recognizing the foolishness of actions of others is a critical feeling in advancing the practice, piti resulting from insight. This is the source of the greatest form of joy (SN 36.31).
Whenever I read this line, I imagine myself doing something, but then someone taps me on the shoulder and asks for my help and I put down what I am doing and go and help out. This to me is ‘not busy with duties’. 