This is the 728th most frequent Swedish word.
mesta
"Most" or "the majority of."
In this usage, 'mesta' qualifies a general term ('förberett'), indicating the extent or majority of preparations according to a personal preference.
De flesta tycker om att ha det mesta förberett.
Most people like to have most things prepared.
Here, 'mesta' functions as an adjective modifying 'möjliga energi', stressing an emphasis on the utmost level of energy or effort.
Mesta möjliga energi bör läggas på detta projekt.
The maximum possible energy should be devoted to this project.
Here, 'mesta' acts as a pronoun referring to the majority or largest part of a specified entity, in this case, 'arbetet' (the work).