The first and worst kind of worship is the hypocrite’s. Popular worship is the second kind. The third kind is the only kind of worship that Jesus values (John 4:24).
Jesus attacked the hypocrisy of the Jewish religious leaders of his day. After calling them “hypocrites” he quoted Isaiah who prophesied against those who worship with their lips but not with their hearts. They say what sounds righteous and worshipful, but they don't truly believe or mean what they say (Isaiah 29:13).
When songs are sung there should be "melody with your hearts" (Ephesians 5:19). And likewise, our hearts must be in our worship when prayers are offered, and the scriptures are read. Worship should not be mere “lipservice”. It must come from the heart.
Furthermore, the heart should agree with the lips. Worship should follow a form, but not be merely a form. Our worship of God and obedience to him must be "from the heart" (Romans 6:17).
Imagine a husband says to his wife, “I love you Darling, you are everything to me,” but all the time he is having an affair. When his wife finds out, will she think he meant in his heart what he said? Will she treasure his words?
God has no time for someone’s fine words and righteous display, when that person’s heart is far from him.
Isaiah points out two faults: firstly a false reverence, and secondly following doctrines of religious rulers instead of God’s own word (Isaiah 29:13b). Jesus, in paraphrasing Isaiah, draws out these two faults.
The worship, Jesus says, is "vain" or valueless, and it follows "tradition" instead of truth (Matthew 15:9). In this worship, the heart may be sincere, and the obedience enthusiastic, but the heart is not in the right place and the obedience is not following the right path.
People invited to a wedding are often informed of the gifts that would be appreciated. What if they all ignored this, and, with the best of intentions, bought instead whatever they liked, and what other people agreed was good? Would the bride and groom be pleased?
God is not pleased with worship people offer who please themselves. They may like and enjoy the worship, but does God? When he has given us his teaching and instruction on what worship to bring, do we expect him to gladly receive instead what we think fit, or what others have taught us?
When Jesus spoke to the woman at the well, he put the two concerns about worship very simply. True worshippers "must worship in spirit and in truth" (John 4:24).
When Moses was preparing worship for the people, God said to him, "Be careful to to make all things according to the pattern shown to you on the mountain" (Hebrews 8:5).
Moses and his people were the worshippers, but they did not invent the worship. If we invent worship as we please, it will be no more acceptable to God than was Aaron’s golden calf (Acts 7:41).
Our hearts should genuinely desire to worship as God teaches. Scriptural worship from the heart is the only kind that counts. That's the standard that Jesus has set.