No amount of reading ability nor knowledge will allow anyone to successfully understand meanings in the Bible without full reading through entire books in the Bible. People *think* they can understand without full reading, and are simply mistaken. (Even reading this full passage of verses 1-20 still isn't enough to truly understand all the meaning it has, but will help much over 1 or 2 verses.)
In Matthew 15:4, we are in the midst of several things Christ says to point out how many legalistic Pharisees tried to substitute their own traditions they made up in place of the actual laws they claimed to be following (and were not in essence following). He points out how serious the old Law was (the law being replaced by His new covenant), and how they were distorting that old Law into their own meanings that weren't the law.
Which still happens today in a new way that is parallel though.
Many distortions here in forums today of stuff in both the New and the Old Testament (the 'old covenant' from 3500-2500 years ago that is *no longer in force*, and has been replaced by a 'new covenant' about 2,000 years ago) are based on carefully isolating verses out of context (and sometimes even some will choose a translation that helps add confusion and aid in a misimpression).
Such reading without context (without reading full books) can sometimes even make something appear nearly opposite what it means in context of that situation it came from. And even with full context and clear meaning, plenty in the Old Testament (and New) still much won't make sense unless you read more so that you know the text is saying God will resurrect both the guilty and the innocent/forgiven to face very different outcomes in the afterlife.