Greetings,
The brahmaviharas are a result of not having hostility and ill-will in regard to all beings, they are a result of having abandoned the wrong view. Therefore instead of trying to practice them, one should develop the right view, and the factors for the right view do not include ‘doing’ brahmaviharas, because you can’t ‘do’ them. You can only abide (recognise them) in them as a result of understanding ill-will and non-ill will.
The boundless states “performed” or practised are not then boundless, they are limited because you are trying to create them on top of your experience of ill-will, non-equanimity, unfriendliness etc
Having freed oneself from ill-will for example, then your mind has the boundless quality of non-ill-will automatically, without being bounded by you, without having to be performed by you.
The Metta is not a medicine for ill-will it’s the result of not having ill-will.
Of course one should be kind whenever possible, but kind acts do not purify one from the possibility of acting unkindly. Restraint and understanding of the non-doing of unwholesome actions will reveal your limiting choice, your responsibility in acting unwholesomely or not. Simply not acting out of ill-will and fully understanding what ill-will is based on, can reveal the boundless nature of non-ill-will and recognising that one abides ‘divinely’ / like Brahma.
It is a divine abiding because you do not ‘do’ it or create it.
You can only recognise it, and keep recognising (being mindful) until the mind turns away completely from that which is limiting i.e self, conceit, ill-will, hostility etc.
Stop doing unwholesome and look what is left…the effortless wholesome, which doesn’t need your input.
This is why the Brahma viharas can lead to arahantship because the knowledge of anatta can be understood through them.