If you want to show some text or message using CMS block below Order Summary section on Checkout Page, then follow below steps.

Step 1 : Create file like app/code/Magemonkeys/Belowordersummary/registration.php

<?php

    MagentoFrameworkComponentComponentRegistrar::register(
    MagentoFrameworkComponentComponentRegistrar::MODULE,
    'Magemonkeys_Belowordersummary',
    __DIR__
    );

Step 2 : Create file like app/code/Magemonkeys/Belowordersummary/etc/frontend/di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="MagentoCheckoutModelCompositeConfigProvider">
        <arguments>
            <argument name="configProviders" xsi:type="array">
                <item name="cms_block_config_provider" xsi:type="object">MagemonkeysBelowordersummaryModelCmsConfigProvider</item>
            </argument>
        </arguments>
    </type>
    <type name="MagemonkeysBelowordersummaryModelCmsConfigProvider">
        <arguments>
            <argument name="blockId" xsi:type="string">checkout-cms-block</argument>
        </arguments>
    </type>
</config>

Step 3 : Create file like app/code/Magemonkeys/Belowordersummary/etc/module.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Magemonkeys_Belowordersummary" setup_version="1.0.0"></module>
</config>

Step 4 : Create file like app/code/Magemonkeys/Belowordersummary/Model/CmsConfigProvider.php

<?php
    
    namespace MagemonkeysBelowordersummaryModel;

    use MagentoCheckoutModelConfigProviderInterface;
    use MagentoFrameworkViewLayoutInterface;
    use MagentoStoreModelStoreManagerInterface;

    /**
    * Class ConfigProvider
    * @codeCoverageIgnore
    */
    final class CmsConfigProvider implements ConfigProviderInterface
    {

        private $layout;
        private $storeManager;
        private $cmsBlock;

        public function __construct(LayoutInterface $layout, StoreManagerInterface $storeManager, $blockId)
        {
            $this->layout = $layout;
            $this->storeManager = $storeManager;
            $this->cmsBlock = $blockId;
        }

        public function getStoreId()
        {
            return $this->storeManager->getStore()->getId();
        }

        public function constructBlock($blockId)
        {
            $storeId = $this->getStoreId();
            $block = $this->layout->createBlock('MagentoCmsBlockBlock')->setBlockId($blockId)->setStoreId($storeId)->toHtml();
            return $block;
        }

        public function getConfig()
        {
            $cmsBlock = '';
            $blockId = $this->cmsBlock;
            if (isset($blockId) && $blockId != '') {
                $cmsBlock = $this->constructBlock($blockId);
            }
            return ['cms_block' => $cmsBlock];
        }
    }

Step 5 : Copy file sidebar.html in your theme from vendor/magento/module-checkout/view/frontend/web/template/sidebar.html

Add this code in your sidebar.html

<div class="opc-block-shipping-information">
    <div data-bind="html: window.checkoutConfig.cms_block"></div>
</div>

That’s it…

Now, you can check your Checkout Page. It will show your text or message which is set in static block as displaying below Order Summery section.