1) The woman says that she knows "Messias" is coming, and that he would "tell us all things". True, but she apparently thought "all things" ended with Jesus revealing what he knew of her. Therefore, she tells the men "he told me all the things that I ever did" and asks "is this not the Christ?" What had she previously been told about the Lord; did she understand it? Did she know he would be put to death for her sin, so that she might be spared that awful penalty? Who, or What, did she think "Messias" was?

2) The Lord isn't speaking to the woman as much as to us, who read and study His Word. He is, I think, saying "ye worhip ye know not what" because many don't fully comprehend duty before Him, as His servants.

3) Transcending time, and therefore being always contemporaneous to every age, the message that is needful is focused upon in verses 23 & 24. We that are saved by His blood are His; our duty is to spread the news of salvation to all possible, clearly, simply, without encumbrances or falsehood.

The whole passage, from verse 7 to 29, can be read as an illumination of the need for proper and true witnessing in the Lord's Name. Look at verse 27 for confirmation: "What seekest thou?"- why, salvation for all (For God so loved the world...); and "Why talkest thou with her?"- because the Good News is to be shared, not kept to oneself.