Great Question! A lot of people are confused by this. They are different marketing tools but can work together easily.
Your weekly Ezine (Electronic Newsletter) is the tool that you actively send out from your autoresponder every single week at the same day & time to your client and prospect lists. You maintain (and consistently grow) your email lists, create the personal greeting and feature article for your Ezine each week, format everything in your template so it is branded to you and looks pretty, and push “Send”. The purpose of the Ezine is relationship building and staying top-of-mind with the prospects and clients that have opted in to your list.
Your blog (if you have one) is a separate entity with its own URL (or can be a page on your website) that you create and post periodic “updates” to. You don’t actively have a “send” button here. You are hoping that people out in the big bad world will search online for some keywords that will bring them to your blog and that they will click on it, read it, love it and sign up to be notified in the future when you post a new blog article/update. The purpose of the Blog is twofold: 1. To attract new interested prospects through their online searches and 2. To relationship build with those who follow your blog and convert them over to your prospect list.
So those are the differences, but the good news is that you can repurpose your feature article from your Ezine every week and use it as your blog post for that day. You are basically getting double-duty out of your writing efforts! Having both does not require double work.
So, get writing!