The the_ID() function that you are using in your code echos the current post id, to get current post id instead of displaying it use the function get_the_ID() as shown in the following code.
Alternatively you can just use get_post() function without passing any post id as a parameter because the post id parameter is optional and if you don’t pass any post id then by default the current post is used.
Try using the following code instead of what you are using.
<meta name="description" content="<?php $post = get_post(get_the_ID()); echo strip_tags(substr($post->post_content,0 , 150)); ?>">