M2: Add a CMS block to your layout

Add a CMS block to your layout XML:

<referenceContainer name="containerName">

    <block class="Magento\Cms\Block\Block" name="block_name_in_layout" as="block.name.in.layout">

        <arguments>

            <argument name="block_id" xsi:type="string">block_identifier</argument>

        </arguments>

    </block>

</referenceContainer>