“Word” here is a metonym for “Jesus.” AT: “God’s Message to mankind” (See: rc://en/ta/man/translate/figs-metonymy).
Here “flesh” represents “a person” or “a human being.” AT: “became human” or “became a human being” (See: rc://en/ta/man/translate/figs-synecdoche)
The phrase “the one an only” means that he is unique, that no one else is like him. The phrase “who came from the Father” means that he is the Father’s child. AT: “the unique Son of the Father” or “the only Son of the Father”
This is an important title for God. (See: rc://en/ta/man/translate/guidelines-sonofgodprinciples)
“full of kind acts towards us, acts we do not deserve”
John is speaking about Jesus. The phrase “comes after me” means that John’s ministry has already started and Jesus’ ministry will start later.
“is more important than I am” or “has more authority than I have”
Be careful not to translate this in a way that suggests that Jesus is more important because he is older than John in human years. Jesus is greater and more important than John because he is God the Son, who has always been alive.