何事も最初は難しく、やがてやさしくなる。
All things are difficult before they are easy.
I've never seen an い-adjective used in this way (難しく). Would using 難しくて (which is what I would have used) change the meaning of the sentence?
There are two ways to form sentence conjunctions using 用言{ようげん} (inflectable words) in Japanese sentences:
It is called the 中止形{ちゅうしけい} when you use the 連用形 as a conjunction.
Nuance-wise, using the 中止形 is a little more literary, so it can give a more formal feel to the sentence.