This verse is much shorter in Greek. A lot was added to the KJV translation, both in the Greek to English translation and in the Greek source, which was translated from the Latin rather than the original Greek source that we use today. In looking at this and related verses, it seems as though the translators may not have liked Christ's message here and were working a bot to obscure it.
The last part of this verse ("of God") copies the ending in Matthew 15:3 exactly, but Jesus changes the word translated as "commandment" here. This is an example of Jesus repeating phrases, usually for humorous effect.
Christ's Words in Matthew as a Guide to 40 Days of Prayer.