When our worship is insincere, we are just going through the motions. We may be singing praise to God but, because our hearts are far from Him, the words that come out of our mouths are nothing more than lip service (Isaiah 29:13; Matthew 15:8). We are worshiping simply because it is expected of us. It's what we're supposed to do. But, it is worship that is in vain. It is neither hot nor cold. It is lukewarm. Just as works done with a heart that is lukewarm, so lukewarm or insincere worship will make the Lord want to spit us out of His mouth (Revelation 4:15-16). Insincere worship is not true worship.
When we worship without humility, we are worshiping to make ourselves look good. We are looking to impress those around us. When we worship in this way, our worship lacks the reverence it requires. Our worship should be vertical and not horizontal. It must be directed to God and not to those around us. In Matthew 6:5, Jesus taught that, when we pray, we are not to be like hypocrites who do so in a manner to be seen by others. This holds true when it comes to worship, as well. Worship done to impress others is not true worship.
When we worship only through formal acts of worship, but not with our lives, our worship costs us nothing. Worship is not just singing our songs of praise and worship on Sunday. Worship must include living a life that conforms to God's Word. Worship includes giving sacrificially of our time, talents, and treasure. God desires worship that involves our whole lives. He desires worship that is costly for us, worship that is marked by a life that does not conform to the world, by a life that is transformed by a renewal of the mind (Romans 12:1-2). It is worship that is a living sacrifice to God. Worship without cost is not true worship.
So, true worship is sincere. It requires all of our heart, not just part of it. True worship is done in humility, vertical worship done for God alone. And, true worship is costly. It involves offering our whole lives to God, not just a part of them. True worship is worship offered in spirit and in truth (John 4:23-24).