I have to write an essay about specific topic of the importance of teaching vocabulary to EL, could you help me to find one or just give me an examples ?

Sure, well first, I'll make the assumption that by "EL" you mean "English learners." And it really goes without saying that teaching vocabulary is important in learning any second language as the lexicon is one of the two main components of any language along with the grammatical system. Opinions differ on how best to teach vocabulary, some favoring a traditional, rote-memorization approach largely separated from actual communicative context, while others maintain that the only effective way to teach vocabulary is the same way that people learn the vocabulary of their first language, through real-world interaction. Proponents of the latter approach, however, tend to overlook some of the special situations and needs of second-language learners, such that perhaps an integrated approach is best, i.e., one where explicit instruction in vocabulary items is often if not absolutely necessary then at minimum highly desirable, without losing sight of the essential utility of any human language and thus the ideal goal of second-language learning and instruction, to foster learners' ability to communicate in the real world, incorporating both expressing one's own thoughts as well as comprehending the language of others in appropriate contexts.