Leviticus 8-10
These chapters begin the study of the consecration of Aaron and his sons.
They were the priest appointed by God and revealed to Moses. Aaron and his sons were to be consecrated and perform the duties of the tabernacle. Every duty and responsibility is carefully outlined by God himself and spoken to Moses to be revealed to the priests.

Aaron and His Sons Consecrated - Lev.8:1-36

The Priestly Ministry Begins - Lev. 9:1-22

The Profane Fire of Nadab and Abihu - Lev. 10:1-7
Conduct Prescribed for Priests Lev. - 10:8-20

Right or Wrong Ritual: Life or Death (Lev. 10:1-7)
In the modern western world we tend to think of religious rituals as the procedures by which a group of people worship God. It is not a crisis of faith if some part of a ritual is not done exactly right. But in the ancient world the ritual was considered something to be performed correctly. The ritual properly performed, was proper religion. To make an error in the prescribed forms of the rite was not just a mistake, but an act of impiety.

The priests, who were anointed and set apart to perform the rituals, were expected to live by a more stringent set of rules than were ordinary people. They had to memorize all the liturgy, hymns,k and words for every religious service. The ancient world held services for the deities every day of the year, and so specialists were needed among the priesthood who could handle any service. These priests, it was believed, were chosen by the deity being worshiped.

Nadab and Abihu, Aaron's sons, were legitimate priests who chose on their own not to follow the ritual that was sanctioned by God (Lev. 10:1). Their deviation appears minor in the eyes of the modern western world; they simply lit their incense censers with a fire from an unapproved source. But for this breach of worship they were both destroyed by divine fire (Lev. 10:2).

Israelites and Judahites would have understood these deaths as the proper consequence. A priest was supposed to follow the proper ritual, since the ritual was the way deity was honored and respected (Lev. 10:3). Nadab's and Abihu's evil was their decision to determine for themselves right and wrong ways to worship. Even mourning for these dead priests was denied, lest it be seen as condoning their sin (Lev. 10:6,7).

I believe that God takes our worship of Him very seriously still today.
This example, though we do not have the demands placed on us today that were placed on them, makes me aware of just how seriously we should look at the process of worship. God says that we should worship Him "in Spirit and in Truth" What does that mean exactly? We are commanded to be "filled with the spirit" in many places in God's word. Perhaps true worship can only be done if we are void of the things of this world and (filled with the spirit). To worship in (truth) means to me, that I will know in my heart the truth of God's greatness, mercy, and grace; when we are aware of these characteristics of God, we cannot help but worship Him in truth.

So, I guess, I would describe worshipping God in spirit and in truth as (The act of being filled with God's spirit to the point where I am keenly aware of His greatness, mercy and grace toward me; and being made aware of this face I am compelled to yield myself completely and be engulfed in worship of Him to the point where nothing else enters my heart or mind.)
Oh to worship God so completely and fully that nothing else matters.
That's how I want to worship Him!!!! How about you?