How to make a clear, relevant post

I've been wondering what I should use this blog for. Should I make this a rambling about the day to day activities of my life? Should I share something from my Bible studies or from speakers/classes that I have been in recently? The only two things I know for sure are:

1. I want this blog to be about doing something for Christ. I may be the one writting it, but I want it to be uplifting and encouraging, perhaps thought provoking and, above all, beyond me. I am not starting a blog just to post new pictures of my daughter (though she is a cuttie).
2. How do communicate in a delayed fassion and make what you are writting about clear, understandable, and relevant (interesting)?

I am a child of the modern era. I have never corresponded my mail. E-mail is, in general, very informal and often shallow. On top of that, it is most often between me and one or two other individuals. In blogging, I will be talking to unknow numbers of people. How do I communicate when one of the basic tenets of clear communication is broken (tell a person something, have them repeat it, and then you repeat what you said to clarify what you meant based on what they heard). Any ideas out there from more experienced bloggers?