The Lord says: “These people come near to me with their mouth and honor me with their lips, but their hearts are far from me. Their worship of me is based on merely human rules they have been taught. (Isaiah 29:13 NIV)
This scripture from the "ancient" book of Isaiah was written at that time about "God's people" - the Jews. Though they professed love and obedience to God, this scripture clearly says otherwise! Oh they obviously went through with the outward appearance of religion. "…honor me with their lips", but the Lord knows who are his (2 Timothy 2:19 NIV).
Before us religious people of today read this and shake our heads at those hypocritical Jews of yesteryear, we should pause and examine our own behavior. It is not uncommon for Protestants (a label that likely would be applied to me) to turn up our noses at say the Catholics or other religions whose expression of worship appear to be built largely on "merely human rules they have been taught". Perhaps we may be right. But I will submit to you that the Catholics have nothing on us Protestants in this regard. I have sat in many a "worship service" and seen the lethargy or outright disinterest that appear to beset the so-called people of God as the ritual of worship is conducted in our so-called Houses of Worship!
For all of us lost and saved sinners alike, the key part of this scripture is the phrase "…their hearts are far from me". The reason why the Lord knows those who are His is because the Lord knows our hearts. The real Houses of Worship is our hearts and bodies. The Bible says that He will put his Spirit in our hearts (2 Corinthians 1:22).
Examine your heart. When you are worshipping God, are your lips moving (or hands clapping) but your thoughts are elsewhere i.e. what's for lunch? what time's the ballgame today? back to work tomorrow! etc. Does your heart stop you from responding harshly to your neighbor when they have ticked you off? How about stopping you at the edge of lying when doing so will get you out of a jam? Worship is not just for the church service on Sunday mornings. It is a 7-day a week activity often during the routine things of our lives. Let's examine ourselves indeed.
Remember: the Lord does know who are His!