The book of John was penned by him with an audience in mind; to the Gentiles and also Hellenistic Jews . His choice of using the "word" was to convey a message. The message was that the Word(Jesus) was present at the beginning, He is God and was with God. It was to inform them that's Jesus Christ is indeed God.
John also wanted to show something more about the nature and ' function' of the eternal Son. So he called him “Ho Logos.”
Ho Logos literally means “the word,” but to the Greek mind it also represented “Reason” in the Ideal sense.
From History, it's believed that the first man to contemplate an ultimate “knowledge,” or “reason” which could be described as Ho Logos, was Heraclitus 500B.C.(His name is even mentioned in the strong's concordance for the translation of Logos). Heraclitus saw the Logos as a “message” which the world (cosmos) had to offer. It was not simply a literal message, but rather “the reason things are as they are," like why the moon is the way it is, the sun(it's brightness, heat and radiance etc).
Later the Stoics expounded this message (which has been mostly perceived as logos) and concluded that the universe is made up of; matter(or the physical component) and another sort of force ordering and organizing the universe into place. To them this force was some sort of energy that brought all creation into order. This was their logos.
Later on, a sect of Jews who grew up with the mosaic law sought to integrate their knowledge of the law, their culture with Greek philosophy. One of these men was Philo who reasoned that Logos was not merely a force but God's Own reason. Some ancient scripts show that he called Logos-"God's firstborn son". Philo said that the cosmos was so ordered because God's Reason ordered it.
He acknowledged though that God's reason is infinite but Logos wasn't a person or being. Philo's teaching impacted many Jews(esp the Hellenists).
So John knowing his audience of Jews and Greeks, sought to Counter the radical claims about Logos depicting that Logos was not a mere force but in fact The Son of God-Jesus Christ who took on human form. Logos was the person of Jesus Christ. That the very thing that enervates the universe was dwelling among men(John 1:14). He preached a gospel proclaiming that Jesus Christ through whom all things were made had been seen by him and many other men(who didn't acknowledge him).