About This Answer
A meditator who was taught to use mettā as a way into jhāna asks whether this misses the spirit of mettā, which seems worth cultivating simply because loving-kindness is beneficial in itself for oneself and others.
Ajahn Dtun replies that mettā develops goodness in one's own heart and helps overcome anger towards others, and it can be used to make the mind peaceful. But it cannot take one to the very end of practice. Someone who cultivates it will be slow to anger and will rarely feel anger, yet mettā alone will not rid the heart of anger completely.
To uproot anger, one has to contemplate the body: the practice of asubha kammaṭṭhāna, the unattractiveness of the body, or contemplation of the four elements, seeing the body's impermanence, unsatisfactoriness and absence of self. Only by doing this can all attachment to the body be removed, and with that, all anger let go.