What are crawling and indexing?
Crawling is Google fetching your pages; indexing is Google storing and understanding them. A page that is not indexed cannot rank, however good it is.
Before a page can rank, two things have to happen to it, and they are easy to confuse. Crawling is Google finding the page and fetching it. Indexing is Google processing that page, understanding it, and adding it to the collection it ranks from.
A page can be crawled and not indexed. Google may decide it is a duplicate of another page, that it adds nothing new, or that it simply is not worth keeping. It can also be blocked from either stage by mistake: a line in the robots.txt file stops crawling, and a noindex tag stops indexing, and both turn up on live sites far more often than they should.
The quickest way to see what is happening is Google Search Console, which reports which pages are indexed and, for the ones that are not, the reason why. If an important page is missing from search altogether, this is the first place to look, before any conversation about content or links. A sitemap helps Google find pages, but it cannot make Google index them.
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