You can think of decoding as word recognition. When decoding is effortless and automatic, word recognition is also automatic. The child doesn't have to think about each word in turn, so he or she can listen to what the author is saying.
By contrast, when word recognition is slow and challenging, the child spends so much time thinking about what each word...
what sound each letter makes,
which letters are silent,
how those sounds are ordered, and
how they blend together,
‑that he or she can't consider what the author is saying, so every sentence seems meaningless.
As decoding skill begins to take root, zero comprehension is actually normal. If you close your eyes and listen to your child while he or she is in this phase, you'll discover you can't understand what is being read either. Whereas your child was too busy thinking to listen to the author, you're having trouble because of an obscure memory phenomenon. It's too complex to explain here--but it's important. It's one of the six reasons almost no one in this country reads for fun.
Three of those six reasons are found in the architecture of memory itself. Understanding how and why memories grow makes curriculum design a lot easier. It turns out that memory is a fractal, built from various sizes of a shape that is seen at all magnifications. The subject makes for a rather fascinating rabbit hole.
If height varied the way decoding talent does, some of your acquaintances would be taller than a house. Others would be shorter than fire hydrants. I'd like to tell you that I've found a way to teach even the shortest students. I haven't. Anyone who tells you that she can teach "any" child to read is just lying. Here's what I can say: If your child is a beginner, the odds are about 80% that he or she will finish learning to read within 99 hours. Children who are well below average might finish within 200 hours or so. (Because outliers are rare by definition, I can't yet provide firm statistical estimates of how many finish within 200 hours). Fast learners finish in about 36 hours. The fastest ones already know how to read when I meet them. Some of those start by correcting their parents during bed-time stories. Amazing.
Yes it is a long time, but consider this: One of the bigger school districts in my area struggles mightily to teach its children to read by the end of third grade. They succeed about 50% of the time. They start with sight-word "memorization" in kindergarten. Over the next four years, they lavish about 20,000 dollars worth of daily drill on each child (2 hours a day). In the end, many students find they can read fairly well but they still don't...   like reading...  because they associate it with years of tedium, coercion, error, and frustration. Even as adults, they can't imagine reading being "fun." They read only when it can't be avoided.
If you've read this far, you're one of the lucky 10 to 20 percent of adults who actually enjoys reading. You have passed many of those genes on to your children, so your child is likely to learn to read rapidly and easily, especially if he or she learns reading from me or one of my proteges.