Why did Jehovah institute a formal worship (the Mosaic Law) of himself after Israel exited Egypt? When God put Adam on earth, obedience was all that was asked. Although the details of the conversations in the Garden are not recounted, they seem to be more of a father/son relationship. Then, when Jesus came to earth, he boiled down the formalistic worship into a mere two concise details recorded at Matthew 22:36-40. So why the formal, ritual-filled worship?
One possible explanation may be that the post-exilic Israelites had been deeply influenced by religious practices that existed in Egypt. Animal and sex worship had become common practice. To remove that mindset and merely have a simple father-son relationship with the creator would have left a void that many would have been inclined to fill with pagan worship rituals. So Jehovah gave them a precisely defined practice that would not only answer the question of what God considered acceptable but also provide insight into the prophecies leading to the greater fulfillment (Christ's sacrificial death and the restoration of earth into God's son-ship). Also not to be forgotten is that Jehovah wanted to make sure the Israelites never forgot how he saved them from the clutches of Egypt. (Exodus 13:14-16; 31:13)
But if God never really wanted ritual, why are there passages indicating that even the angels engage in a sort of ritual worship? Although the angels are pictured in some scriptures as "worshipping" and calling out ‘holy is Jehovah,’ those visions were given to mankind to help us appreciate the total devotion and uncompromising loyalty those angels have toward God. Taking the scriptures as a whole, the overwhelming evidence is that God would much prefer to have a close, endearing relationship with us as his children rather than a distant and cold, authoritarian relationship. God is not so self-centered in that he enjoys having his creation call out random praises to him just because he is God.
So rather than the angels mindlessly engaging in formalistic rituals, what is closer to reality is what some accounts help us appreciate about the natural expressions we humans have made and can make. For example the spontaneous expression of praise to God after the Egyptian pursuers were destroyed in the Red Sea while all Israel stood delivered and unharmed in the far shoreline. (Exodus 15:1-21) Or the prophetic account in Revelation 7:9,10 where those delivered through Armageddon are praising God. Likewise, even the angels are awestruck with Jehovah's creative abilities as shown at Job 38:7 (and surrounding verses). Yes, our amazement over Jehovah's power, coupled with his qualities of love (as from a father), wisdom, and uncompromisingly fair justice, are rightly to be acknowledged just as an artist's work is appreciated by others. (Psalms 8:3,4)
So the Mosiac Law helped to organize and standardize a form of worship that would demonstrate what spiritual purity entailed as well as act as a tutor leading to the Christ. However, once it accomplished its purpose, and after it was fulfilled by Christ’s better covenant, we are helped to appreciate the beautiful way God cleverly, gently, and gradually educated mankind to the point of maturity. Someday, we will finally arrive back at the point that Adam started with.