First of all, this is not one, but two questions phrased as one. Allow me to re-phrase this as two questions:
Why Does God Demand That We Worship Him? Or Why does God demand our worship?
Why Does God Seek or Request That We Worship Him?
Does God Demand Worship?
The answer to this first question is that God does NOT demand that we worship Him. In fact, He does not require anything of us! I'm sure that this is a surprise to many, but in the book of Acts, there's text that pretty much states this very point. It says:
King James: God that made the world and all things therein, seeing that he is Lord of heaven and earth, dwelleth not in temples made with hands; Neither is worshipped with men's hands, as though he needed any thing, seeing he giveth to all life, and breath, and all things;
NIV: The God who made the world and everything in it is the Lord of heaven and earth and does not live in temples built by human hands. And he is not served by human hands, as if he needed anything. Rather, he himself gives everyone life and breath and everything else.
Good News Translation: God, who made the world and everything in it, is Lord of heaven and earth and does not live in temples made by human hands. Nor does he need anything that we can supply by working for him, since it is he himself who gives life and breath and everything else to everyone.
Notice two important points revealed in these texts:
Point One, God does not require or even need anything from us to complete or add to His existence - He is self contained - self sufficient.
Point Two, in the relationship between God and man - God is not in this relationship to demand, require or receive anything from us - He is in this relationship solely as the giver. WE are the recipients! He is attempting to give US something! I'll say it again: He's the giver - we are the recipients.
We are not pursuing God, He is pursuing us. This is the very theme of the Bible! (Boy, have we got things backwards!)
Does God Seek or Request That We Worship Him?
In a word, "Yes"!
I know, you're confused now. Right?
Let me explain.
The problem is in how we view the word worship as it applies to God. The conventional and traditional definition of worship - a formal or ceremonious rendering of honor and homage paid to God or a sacred personage - does not apply when talking about true Bible worship. In this definition we are paying homage to God with our actions hoping to please Him. We are doing the work. We are putting fort the effort.
This is not the type of interaction God wants to have with us, or us to have with Him.
A more accurate definition of worship, as it applies to God, would be more in line with these:
To give over or yield to the power or authority of another.
To yield oneself to the power or authority of another: to submit to a conqueror.
To defer to another's judgment, opinion, decision, etc.: submit to superior judgment.
In reality, each of us are free to do with our lives as we please - good or bad! God gave each us that right. He would never demand our allegiance.
God is actually trying to convince us to allow, to give, Him first place in our lives - so that HE can do something for us.
Note that God initiates worship, here! In this scenario God is trying to get us to willingly submit to Him - and that's because He feels (actually knows) that what He has to offer to us is much, much better than what we already have or could ever do for ourselves.
The problem He faces is that, by birth (since The Fall), we don't know, nor do we care, who He is or what He has to offer. That's why He provided (gave or presents to) humanity something called the Bible, a book He knows is good for us. This is He way of (re-) introducing the (now fallen) human race to who He is, what He's about, what He (alone) knows, and what His plans are.
His hope is that you and I would give Him an opportunity to talk with us individually: "Come let us reason together, saith the Lord" (Isaiah 1:18). If you allow it, He will open the eyes of your understanding to "things" you would never find out on your own. He will tell you His grand and wonderful plans. Plans that He wants to involve you and I in - but only if we allow it. Remember, you are free to choose! God would never demand that you take advantage of this opportunity.
He wants to give you good things - but He needs your permission! He needs you to freely submit to His superior goodness, wisdom and plans - submit because you've allowed Him to opened your eyes to a better reality. And because of God's efforts, you've freely decided to accept His offer. God can't, and won't, command or demand that you do anything - He hopes that He can persuade or convince (inspire) you to accept His offer because He's helped you see, with your own mind's eye, the good, the wisdom, the light, in it.
Below are words from a song that demonstrate the true Bible worship experience. The song is entitled:
Here I am to worship by Chris Tomlin
Light of the World
You stepped down into darkness
Opened my eyes
Let me see
Beauty that made
This heart adore You
Hope of a life
Spent with You
Here I am to worship
Here I am to bow down
Here I am to say that You're my God
You're altogether lovely
Altogether wonderful to me
Notice how God initiates worship here. He inspires the singer's decision to "bow down" (position of submission) by giving the singer an experience he would never be able to acquire on his own. God "opened my eyes" and "let me see" the singer says, and in response to God's actions he is joyously submitting (bowing) to the One who has conquered his heart.
Throughout the Bible the true worship act always involved the symbolic act of submission - a physical act of bowing in response to actions by God, acknowledging God's Superiority and the bower's willingness to submit to it:
And the man bowed down his head, and worshipped the LORD (Genesis 24:26)
And I bowed down my head, and worshipped the LORD (Genesis 24:48)
The four and twenty elders fall down before him that sat on the throne, and worship him that liveth for ever and ever, and cast their crowns before the throne (Revelation 4:10)
Notice that in every case worship is in response to something that God has said, done or about to do. Again, I remind you that God initiates true worship - not us!
I might add that kneeling to pray is (supposed to be) an act of willing submission to the Superior Wisdom and Goodness of God. And when you understand God's most precious gift - you'll understand the privilege we've been given to respond (or not) in the worship experience initiated by God.
There's another important point that needs to be made here: Praise and Worship are two totally distinct and separate acts. They do not happen at the same time - they do not go together! In fact, true worship precedes true praise. Or, praise is a response to the worship experience.
True worship, resulting in true praise, involves (1) God making first contact (this is important), informing you of His love and plans for you, (2) your free will acknowledgment of acceptance of His plans, followed by (3) God assuring you that the covenant bond now in place between you and Him, where He promises to give His life to save yours, is real and locked in. Then, lastly, (4) the spontaneous response of praise from your lips for God's graciousness and goodness. Note here that praise is not demanded - its a natural and spontaneous response to God's overtures. In truth, we don't give praise - we are actually responding with praise - responding to something God has done.
Praise, then, is a glorious response to a wonderful, real and personal worship overture from God.
Remember, God is here solely to offer His help (not to demand anything). Each of us have the right to refuse. But if we say yes, willingly submit (worship), that opens the door for Him show you things beyond our world of darkness that He has made available to us. For you see:
True worship is not about what you do for God, but what you allow Him to do for you.