The last part here seems to be where you get into the purpose of the Sabbath so that's the part I'll comment on since that's the explicit request of the OP so I won't be commenting the on other stuff.
To me it seems like you have described the purpose of us the creation, which is to essentially worship and give glory to God in all things.... broader goals of Christian living as a whole and not on specific goals for the Sabbath. So I'll ask you to dig a little deeper and as promised in the OP I'm asking a why.
Why is the Sabbath conflated with a day?
Why is this day about honoring God, turning from our ways and pleasure and keeping our thoughts and actions towards our Lord and other days do not have this focus?
Why is it about having an appointment every seventh day for communion time with our Lord and Savior when another day is not about this focus?
The arbitrary legalistic aspect is a common misunderstanding. It is "a day" and more. It's a day of surplus/plenty, pointing to the 7th or divinity in all creation. Shmita, sabbatical year of rest on the 7th year, 49th year of jubilee, etc. Cycles of seven and concepts of holiness, throughout Scripture, in mathematics, building & architecture, anatomy, genetics, DNA, science and astrophysics. It's about heaven, and man's involvement/inclusion.
Your implicit point is valid: Constance and regularity vs merely "one day". To "pray without ceasing" and "love the Lord thy God with all", "to take up your cross daily". That is true, in intent, of the heart. Except "The heart is deceitful above all things, and desperately wicked" (Jer 17:9) This is the danger or
individualism without consulting Scripture, also
Spiritualism. An imagined man-made belief, contradictory to God's expressed will.
The purpose of Sabbath is a reminder/remembrance of redemption, symbolically, metaphorically, legally, and actually. It commemorates and aligns the person with God who first rested from his work in Genesis, it's an act of allegiance and affinity. To be holy as he is holy, to do as Christ did.
"And
remember that thou wast a servant in the land of Egypt, and
that the LORD thy God brought thee out thence through a mighty hand and by a stretched out arm: therefore the LORD thy
God commanded thee to keep the sabbath day." (Deu 5:15)
This is ofc difficult to impossible for Gentiles to understand or accept since we never saw this, we never lived this, and our ancestors certainly never went through this. In fact, we are likely the perpetrators, of cain, of Babylon, Egypt, and Rome. Thus, having the same ideals and practices as the Egyptians, that God hated and condemned. This is perhaps why so many people mis-understand "Sabbath" as about "work" and "rest" as if synonymous for "pleasure" and "punishment". But for someone who understands that this world is cage, that work is hard, and that our parents/employers/government/rulers are often cruel, then God's "rest" is like an oasis. And "holiness" is a divine and royal privilege.
The purpose of Sabbath is liberation. "I am the Lord thy God, which brought thee out of the land of Egypt, from the house of bondage." (Deu 5:6)
The world's culture enslaves others, benefiting off others. But God's is "rich" and his system is "life". There is no competition, no misery, no deceit.
The "labour" part is commonly misunderstood as
mandatory forced labour, but if you study the Exodus the people simply had
opportunity to gather
manna and
quails (free food, clean and holy food). "I will rain bread from heaven" (Ex 16:4) The strong and fit would gather and there would be enough for the sick and unfit. There was no conflict of interest. No struggle. No blaming or marginalising. And each man had his fill, regardless of how much he gathered. Whereas in Egypt, they had lived 3-400 years of brick-making quotas, with insufficient ingredients/materials/inventory to do their job properly. Plus they were blamed, scapegoated, and persecuted. Which is a constant theme in the history of the industrial "built" world, thousands die at the expense of building walls and cities for Kings/emperors. So Sabbath is God's reminder, his lesson, that his "way" is truly the path of life and peace.
"This is the thing which the Lord hath commanded, Gather of it every man
according to his eating, an omer for every man, according to the number of your persons; take ye every man for them which are in his tents. And the children of Israel did so, and gathered, some more, some less. And when they did mete it with an omer, he that gathered much had nothing over, and he that gathered little had no lack;
they gathered every man according to his eating. ...This shall be, when the Lord shall give you in the evening flesh to eat, and in the morning bread
to the full." (Ex 16:16-8)
Iow, perfect
market equilibrium in supply and demand, for both goods and labour. Unlike modern Capitalism, working more is done to benefit self and others, and demand is always met. No clutching at straws. There is never shortage, no boom and bust, no outliers or wings, no bulls or bears. No hoarding or greed. No poverty and theft. No room to covet. Everyone has enough. For 40 years there was plenty for all. Also no inflation, deflation, or depreciation. The 'market' refreshes itself automatically, daily. And on Friday there's enough to gather a "double portion" for Sabbath/Saturday to allow a genuine time for rest. Whereas in our economies,
someone, somewhere, is always on duty forced to work. e.g. power plant, emergency room, etc. But not in God's kingdom.
So the purpose of Sabbath is also a lesson about prayer and faith, true dependence and reliance on God's provision. To "Give us this day our daily bread".
Inversely, Sabbath is also a judgement for the world, for law-breakers, and people who oppose God. There is no "blessing" for work done on Sabbath. It won't be fruitful. We would call it a waste of time, a non-performing asset, or a dead market (black Saturday) or something along those lines. The market collapses. So there's a cyclical concept, and if you study the stock exhange history, every 7 years (shmita, 7th year, God's "release") every stock market will shrink significantly. Following that, historically, the pattern is that nations will go to war. Likewise, working on Sabbath is explicit disobedience, a crime of capital punishment, death penalty.
"Eat that to day; for to day is a sabbath unto the Lord: to day
ye shall not find it in the field. Six days ye shall gather it; but on the seventh day, which is the sabbath, in it
there shall be none." (Ex 6:28-27)
So the purpose of Sabbath is also a framework for the living vs the dead, God's sheep his elect his children vs the reprobate his enemies and children of Satan. It's a depiction of the spiritual war that began when Lucifer rebelled against Heaven, and the future war between Christ and the Serpent/Dragon per prophecy in Genesis.
Hence "salvation is of the Lord" and Christ is "Lord of the Sabbath". "For the Son of man is Lord even of the sabbath day." (Mt 12:8) And "sabbath of the Lord thy God" (Ex 20:10).
Iow,
choosing to work on Sabbath is akin to choosing to gather the forbidden fruit in the Garden of Eden. It's failure to grasp to God's paradise. Like a servant gone rogue. So the Sabbath points to
eternal rest,
eternal salvation, in a new creation, new covenant, new kingdom, and in paradise.
For me, due to mostly to upbringing, I have tendencies towards workaholism and perfectionism, harsh self-criticism and constant feelings of under-achievement. Thus, Sabbath and God's provision is truly good news, refreshing hope. A weekly reminder to stop just stop. It's Friday night, the sun's gone down, and I've worked 15-18hrs all day everyday for God knows how long. And the project won't get any better. And there's always next week. Time for a break. Time to go home. Where true home and rest is only found in Christ, Lord of the Sabbath.
No judgement from me. Each to their own. The historic opposition to Sabbath was prompted by abuse of it, wrongful use. Ceremonial or ritual supremacy, is seen one way or another in all denominations. So you are right in pointing at the heart, as God weighs the heart, but you're also changing the subject to the matter of internalism vs externalism; obedience inwardly vs outwardly.
"Let no man therefore judge you in meat, or in drink, or in respect of an holyday, or of the new moon, or of the sabbath days:" (Col 2:16)
Hence Paul wrote,
"Thou that makest thy
boast of the law, through breaking the law dishonourest thou God? For the name of God is
blasphemed among the Gentiles through you, as it is written. For
circumcision verily profiteth, if thou keep the law: but if thou be a breaker of the law, thy circumcision is made uncircumcision. Therefore if the uncircumcision
keep the righteousness of the law, shall not his uncircumcision be counted for circumcision? And shall not uncircumcision which is by nature, if it fulfil the law, judge thee, who
by the letter and circumcision dost transgress the law? For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh:
But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God." (Rom 2:24-29)
So the purpose of Sabbath
for Gentiles then is less a ritual/ceremonial practice but an abstract or free-form obedience, varying with our circumstances as how and where the Lord called us to believe. I briefly commented about my personal practice in another thread.
Additionally, ime, the
principles in Torah/Pentateuch are universally applicable to Jew or Gentile, or any religious or ethnic group. In Chinese philosophy and culture for example, the dominant group believes
filial piety which often becomes abused as filial tyrany (dictator parents, or children who seize power and abuse elders). Whilst there have been minority philosophers who taught
universal love (towards all people), specifying to do unto others not expecting a return but for the sake of others. So yeah, it's very much possible to be a "practicing Jew" and simultaneously a "Christian", in say communist and confucianist China, or anywhere in the world for that matter. If you know God's word and your heart is in the right place. But in any case, your conscience and the HS will guide your steps.