In the simplest terms worship is giving back to God that which is rightfully His with a thankful heart. For example, God should be praised and thanked for His creation. He is the one that created it, and He made it for our enjoyment. How silly it would be for us to thank man for it. Yet we often try to take credit for things God is doing in our lives as if we are the ones solely responsible. We pride ourselves for being the best musician, or being the one person that is most called on to sing solo's at our church. And we let these circumstances that surround our ability and talent move us into thinking we are better than everyone else. Not So! All the blessing and glory and honor goes to God for everything. Romans 12:1 states that even down to our very lives, we are to give all to God, and that giving to Him is our spiritual service of worship.
When Jesus spoke to the woman at the well in John chapter 4, He told her that God was seeking those people who would worship Him in Spirit and Truth. If we look into the Greek of the words "Spirit" and "Truth", we can gain some insights into what I think Jesus was communicating.
Spirit actually means "rushing wind". The word for spirit, "pneuma" means "wind" or "spirit" and is derived from the root word "pneo", which means "to blow" and is a root word which is translated Spirit. Worshipping God in the spirit denotes worshipping under His influence or under His control. Basically the first criteria Jesus speaks of here is that a person have a relationship with God. That they have trusted in God's work through Christ for salvation and that they are under His control.
Second, Jesus said that God is looking for people who will worship Him in Truth. The word truth here is "aletheia" which means true, and is derived from the word "alethes" which literally means "to take notice". Jesus was saying that God is looking for His children to literally "take notice of the truth" about Himself.
Worship is specifically accomplished when those that know God, take notice of all that is true about God. Worship is grounded in truth! The more we know God the deeper our worship will take us. Our worship must never be based on anything except the truth of God. Those that worship solely for the experience, or to be noticed, or to gain recognition, or for traditions sake are missing the mark.
Worship is not merely following a church program through the service. God continually looks to the heart of men to see if what is being offered to Him is genuine, and not some tradition that is performed for selfish reasons.
Isaiah 29:13-14 reads: 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 made up only of rules taught by men. Therefore once more I will astound these people with wonder upon wonder; the wisdom of the wise will perish, the intelligent of the intelligent will vanish."
Where is your heart as you lead worship, and where are the hearts of those you lead? It is a question that we should know the answer to.