unique glory

John uses this paragraph to gives us more words, both images and concepts, which describe the person he is telling us about.  Just like the previous ones, most of these words, and all of the ideas behind the words, will echo through the narrative to come. 

The key words here are "full of grace and truth" - but before he comes to this phrase, John takes trouble to point out yet again that this person is unique; he is the one and only who came from the Father.  This is an interesting phrase, and we struggle a bit in English because there is no way of translating it which is a elegant, as poetically pointed, as the Greek which is a single word!
I am generally dead against amateurs like you and me messing with translation because after all, if you get 70 of the world's most expert Greek, Hebrew and English specialists together (like they did to create the NIV) how am I likely to clarify things?  However what I am doing here is IN NO WAY suggesting an alternative translation, but merely explaining for interested parties why it might sound less elegant than expected, and why some translations use that odd device of adding in the word [Son] - the square brackets mean that it is a word added for clarity, which the translators believe is 'understood' in the original.  So, this is just my way of teasing out what John is telling me!

This word is a composite one:  The first part is mono, which is totally familiar to us because we use it in much the same way in English, tells us this thing is the only one, or one-of-a-kind.  It is fairly simply translated as "only" or "one and only".  The second part is the tricky bit it is genos (or at least genous, which merely another part of speech for the same word, like the differerence between love and loved - same meaning but changed form to fit into a different part of a sentence) which has to do with someone being descended from another person, or perhaps a thing which is the same as another and emerges from it.  So an old translation uses the word "begotten" of the Father, which we don't use any more.  Our NIV 2011 says "Son who came" from the Father.  But some people struggle with the idea of Jesus as God's Son because it sounds too biological, too earthy.  Now later John will use the normal Greek word for 'son' when he will call Jesus the 'Son of God' and invte us to believe that, but he isn't actually doing that yet. Here he is being more subtle, more complex, more abstract.

I think here   John is trying to portray that Jesus is someone whose relationship with God can't be described in the normal ways.  We've already see this in the first paragraph with the multiple descriptions of the Word with respect to God.  Now he is finding another way of saying that Jesus is 'the same as' God but 'distinct from' God also.  For good measure, in case another is tempted to say, "Oh, well, of course we all come from God, after all he made us," or words to that effect, John puts in the prefix mono.  The only one like this.

It is this glory that John and his companions saw as they lived with Jesus.  This is the glory he is going to tell us more about.  It is a glory which is inherent in the nature of this unique person. As we will see, this glory can be described by the phrase: full of grace and truth.

... an aside on men, women and people

Greek was the language John wrote in, thought he was amost certainly bilingual in Greek and Aramaic, as well as able to read Hebrew.
These languages all have a useful word which English lacks: in Greek it is anthropos and it means a human, as in someone who may be male or female.  In the plural, it means humans, people, without reference to gender.  In English the word 'men' was formerly used in this generic sense and therefore anthropos was translated 'man' or 'men'.  The trouble is, even long ago, though 'men' could include women it didn't give the same gender-isn't-relevant feel as the Greek word, and even more so when speaking of an individual. 
Greek also has words that means specifically man/men and woman/women.

In the New Testament most of the time when our translations (certainly up to the beginning of this century, and even some post 2000) use the word man/men it is translating anthropos, in other words it means 'a person' or 'people'.  This can change the feel of a story, or even more of a symbolic or philosophic passage quite considerably.  This is especially true today, because English has changed (as all languages do) and most people will choose a word without gender-implication where they can.  
Thus, translations of the Bible which are up to date with current language use will try to use gender-non-specific words to translate the word anthropos.  

There are two difficulties. 
First, there are sentences which still don't quite flow well when trying to recreate the feel of "all anthropos", and translators constantly have to juggle with "humans, people, humankind, persons" and it can be tricky. 
Second, the singular is more difficult still, since 'person' and 'human' are sometimes not appropriate.  In this instance the translators very often simply use the words 'man' or 'woman', relying on the context to give them the gender of the person involved.  At times there is no way to convey the sense adequately.

The result of all this is that there are places where the English overemphasises the gender of people involved.  There are times when the flow of thought is undermined because the Greek repeats the word anthropos while the English needs to use more than one word.  There are also occasionally phrases where it is impossible with current English usage to get the inclusiveness or ambiguity inherent in the Greek.

This doesn't mean that we can't understand the Bible.  Most translations really are excellent.  However, if we are aware of this as an issue faced by translators, we are less likely to misinterpret gender as a issue when it isn't.  It also helps explain why your translations might say "men" when mine says "people"!
For a detailed treatment of this issue look at the NIV 2011 discussion of it.  This can be found on the "Biblica" site, which is the website of the former International Bible Society. http://www.biblica.com/niv/accuracy/