You can access the message from a Twig template as follows:

.. code-block:: html+twig

<h2>Publication was blocked because:</h2>

<ul>

{% for transition in workflow_all_transitions(article) %}

{% if not workflow_can(article, transition.name) %}

<li>

<strong>{{ transition.name }}</strong>:

<ul>

{% for blocker in workflow_transition_blockers(article, transition.name) %}

<li>

{{ blocker.message }}

{% if blocker.parameters.expression is defined %}

<code>{{ blocker.parameters.expression }}</code>

{% endif %}

</li>

{% endfor %}

</ul>

</li>

{% endif %}

{% endfor %}

</ul>