lex - is
There are many reasons to learn how to divide lexis into syllables. Separating a word like lexis into syllables is mainly to make it easier to read and pronounce. The syllable is the smallest sound unit in a word, and the separation of the lexis into syllables allows speakers to better segment and emphasize each sound unit.
Knowing how to separate lexis into syllables can be especially useful for those learning to read and write, because it helps them understand and pronounce lexis more accurately. Furthermore, separating lexis into syllables can also be useful in teaching grammar and spelling, as it allows students to more easily understand and apply the rules of accentuation and syllable division.
In the case of the word lexis, we find that when separating into syllables the resulting number of syllables is 2. With this in mind, it's much easier to learn how to pronounce lexis, as we can focus on perfecting the syllabic pronunciation before trying to pronounce lexis in full or within a sentence. Likewise, this breakdown of lexis into syllables makes it easier for us to remember how to write it.