You can use the eq method to reduce the matched set of elements to one at a specific index:
$(this).siblings(".bar").eq(0).text()
That will select the first element in the set. In your case, you could simply use prev, as the element you’re looking for comes directly before the clicked element:
$(this).prev(".bar").text()
The problem with the array notation method you were using is that it returns the actual DOM node contained within the jQuery object, and that’s not going to have a text method. eq is the equivalent jQuery method to do this.