Part VII by Ven. Mahasi Sayadaw
As such, a person who has achieved the third jhana through the development of metta, karuna and mudita, must practise this jhana to become proficient in it. After arising from the trance of that third jhana, he should ponder upon the faults of metta-jhana and so on. It should be reflected as: “These jhanas being closely connected and conjoined with the innermost feeling of loving attachment to beings wishing them happiness, it is linked with love or hate. As it is combined with joy and exultant feeling, the fault of it must be reflected upon and understood as rude and vulgar. The noble faculty and attributes of upekkha should be reflected upon and realised, imagining that upekkhajhana which views things with indifference is indeed gentle and meek. It is stated that only after reflecting as such, upekkha should be developed with indifference towards a neutral person on whom there is neither love nor hate. The manner of developing upekkha is what is generally known by heart as: “Sabbe satta kammassaka” ‘ i.e., this person has his kamma as his own property and that it is his own fate (kamma) to which he has become a victim. After he has achieved the fourth jhana by contemplating as such, he should proceed to develop upekkha towards a person who is affectionate to him and towards persons who are hostile to him. When radiating his feeling towards an enemy, if anger arises in him, it must be subdued in the manner as prescribed in the case of developing metta. After suppressing his anger, one should be able to contemplate with a feeling of indifference, putting the mind equally balanced on all four types of persons including himself, thereby accomplishing the quality of simasambheda. After that, the fourth jhana will occur. This is according to what has been stated in the Visuddhimagga.