<div id="tema">
  <div class="eTitle">1 eTitle</div><div class="eMessage">1 eMessage</div>
  <div class="eTitle">2 eTitle</div><div class="eMessage">2 eMessage</div>
  <div class="eTitle">3 eTitle</div><div class="eMessage">3 eMessage</div>
</div>
 
<script type="text/javascript">

// :TODO: addEventListener/attachEvent

window.onload = function()
{
  var
  holder = document.getElementById('tema'),
  blocks = holder.getElementsByTagName('div'),
  l = blocks.length,
  a = [];

  while(l--)
  {
    blocks[l].style.display = 'none';
    if(blocks[l].className == 'eTitle') a.push(blocks[l]);
  }

  a[Math.floor(Math.random() * a.length)].style.display = 'block';
};

</script>