It is a common past tense construction used to describe something unexpected, a special circumstance happening in the past and transpiring over a period of time. "The discovery of the tomb was to result in his undoing." "No one knew the assassination of the Archduke was to lead to a terrible war."

Since you are using the adverb "incredibly" it means you are describing something that already happened. So in that case I'd rather say: Incredibly some friendships lasted a lifetime. ____________________________________________________________________________ Here are some short English stories to practice your English reading skills. http://easyenglish.today/category/short-stories/

"was/were to" in indicative sentences is a more literary (and somewhat old-fashioned) way of relating what happened. "Some friendships lasted a lifetime" and "Some friendships were to last a lifetime" refer to the same fact, but the latter evokes a faint sense of destiny or historical importance, like "it turned out that way now that I look back on it". Another example might be: - That day was the last time I saw him. (simple fact) - That day was to be the last time I saw him. (implies "I didn't know it then, but it turned out to be ...") And there are some phrases where "was to" is favored over others (regrettable negative outcome with finality) - He was not to be found [seen, heard from] again. - It was a love that wasn't to be. "were to" is also a common form of expressing an impossible or unlikely idea in the subjunctive mood. - If were a millionaire, I would do these things. (subjunctive present - If I were a millionaire now) - I were to become a millionaire, I would do these things. (subjunctive of the near future - If I should become a millionaire)