OP: How can the Word be a Person?
A better question might be, "How can the Λογος be a Person?" As others have pointed out, the Greek term λογος has a much broader meaning than merely "word."
According to Thayer's Greek Lexicon, λογος can mean:
- a word
- a saying
- a speech
- a matter under discussion
- reason (i.e. mental faculty of thinking)
- a cause
I have put "a cause" in bold because this definition seems to me the most fitting of the above for a Divine Person. After all, the Λογος in John Chapter 1 is the cause of the universe and of all created things.
All things were made by him [him = the Λογος]; and without him was not any thing made that was made. (John 1:3)
OP: What is the nature of this Word?
I answer that the Λογος has two natures, a human nature and a divine nature. We see in John 1:1 that the Λογος is God, but we also see in John 1:14 that the Λογος became flesh.
Did the Λογος lose his divine nature when he became flesh and took on a human nature? Not at all. Consider the following verse from Revelation.
Καὶ τῷ ἀγγέλῳ τῆς ἐν Σμύρνῃ ἐκκλησίας γράψον· Τάδε λέγει ὁ πρῶτος καὶ ὁ ἔσχατος, ὃς ἐγένετο νεκρὸς καὶ ἔζησεν·
And unto the angel of the church in Smyrna write; These things saith the first and the last, which was dead, and is alive; (Revelation 2:8, KJV)
The "first and the last" is a title for God (see Isaiah 44:6). Revelation 2:8 says that the first and the last was "dead, and is alive." But God can't die in his divine nature, since he is immutable.
The Λογος is the first and the last, which was dead. The Λογος is the first and the last in his divine nature, but died and rose from the dead in his human nature. The Λογος is God and man simultaneously.
It is mind-blowing and incomprehensible for sure, but that is to be expected with God. (Isaiah 55:8-9)
Recommended reading
To the OP, I would recommend reading about the Ecumenical Councils (especially the first six) in order to understand what the early church taught regarding the Trinity, the Nestorian Heresy, the two natures of Christ, the two wills of Christ, and other important topics.
I also recommend reading the actual documents from these Councils, especially Constantinople II, which recaps and elaborates so well on the doctrine of the two natures defined at Chalcedon.
