Sentence:  ... "Religion" direct us rather to ſecure "inward peace" than "outward eaſe", to be more careful to avoid "everlaſting" and "intolerable torment" than  "ſhort" and "light afflictions which are but for a moment"; ... In a word, our <WSD>"main</WSD> intereſt" is to be "as happy as we can", and "as long as is poſſible"; and if we be caſt into ſuch circumſtances, that we muſt be either in part and for a time or elſe wholly and always miſerable, the "beſt wiſdom" is to chuſe the "greateſt" and "moſt laſting happiness", but the "leaſt" and "ſhorteſt miſery". 
Meaning of the word marked with <WSD> tags:  Of chief or leading importance; prime, principal. (from 15th c.)