_default/list.html enable "Content" of _index.md

layouts/_default/list.html

 {{ define "main" -}}
 <ul class="posts">
   <h1>{{ .Title }}</h1>
+  {{ with .Content }}
+  <div class="index_content">
+    {{- . -}}
+  </div>
+  {{ end }}
   {{ range .Data.Pages -}}
   <li>
     <div class="flex">