More often than not, people get it in their head, that they have a better way of honoring God, than that which God requests and requires.
So, the sacrifices, or the worships, or the motions people go through toward God, are outward only, and not from the heart. The heart represents the circulation of thought in the soul. And more particularly the circulation of doctrine in the soul.
However, the circulation of doctrine, requires a knowledge of doctrine, as well as a dwelling in the fellowship sphere. And knowledge of doctrine requires a daily study in order to learn it.
Most folks do not confess on a regular basis, and therefore are most often living their lives out of fellowship. Likewise, most folks do not participate in a study of any kind, let alone a daily study, and therefore come up with their own ideas of how to honor God.
That is what Cain did, and his sacrifice, his approach, was rejected by God.
So, you can sing all of the songs, quote all of the scriptures, say all of the right things (in public or anywhere), but if you have not follow Gods mandate for studying and learning, and in accordance with His prescribed method for studying and learning, then all of your efforts are for naught. Anything done your own way (by the energy of the flesh), is a useless effort.
Regardless of who you might impress, regardless of your impressing yourself, all things done apart from Gods authorized method, are useless efforts. Even doing them in great quantities as the Israelites were doing here.
Gods mandate is to ‘study to show thyself approved (mature).’ Doctrine is the food for the soul. Food is consumed on a daily basis in order to maintain some semblance of health. Therefore, doctrine must be consumed daily as food is consumed daily. Doctrine must be metabolized properly lest it is rejected by the soul for no value. This metabolism occurs while you are in fellowship. You study, you learn, you accept it, and you benefit by it. You learn, you use, you grow and mature. This is all done while living in fellowship.
Anything else in life gives you zero benefit.
If matters not how loud you sing, or whether or not you know the words to the songs. It matters not how often you attend church. It matter not what vocabulary you use in conversation. It matters not who you are trying to impress. It matter not what you wear or where you live.
If the doctrine is not from the soul, then your spiritual life is dysfunctional and useless.
God is not impressed by your effort nor the volume of your effort, unless you pursue your spiritual life correctly.