This is a part of a series going line by line from the Metta Sutta. It starts here.
Peaceful and calm
It can sometimes seem as though metta and jhana are separate meditative paths. It is not true. In fact, metta meditation is one of the paths to jhana. Every method of meditation described in the suttas goes like this: bring x to mind. Examine x, become absorbed in x. See how absorption in x brings about bliss, happiness, one-pointedness, and equanimity.
Ultimately the meditation goes beyond x into the arupa jhanas. In the case of breath meditation x is the breath. In the cases of dhammas, the meditation is on certain teachings of the Buddha. In metta meditation the object of meditation is the feeling of loving kindness itself. Practicing loving kindness allows us to arouse the experience at will, which gives us the ability to use it as an object of meditation. Which brings us to the peace and calm of meditation. In the commentaries there is a teaching that metta can only lead to the first 3 jhanas but not the fourth. This is not found in the suttas, and I don’t know of any reason that it should be true.
The next article in this series is here.