God is Love.
To love God is to obey the first 4 commandments. And to love each other is to obey the next 6.
Adam and Eve didn't need 10 laws written in stone because they were created in Gods image.
They failed at loving God.
Exo 20:3 Thou shalt have no other gods before me.
The first of the 10 was broken.
Cain killed Abel.
The laws may not have been written in stone but people were guilty of transgressing them.
The spiritual principles were the same.
Rom 2:
14 For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves: 15 Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another.). ....
23 Thou that makest thy boast of the law, through breaking the law dishonourest thou God? 24 For the name of God is blasphemed among the Gentiles through you, as it is written. 25 For circumcision verily profiteth, if thou keep the law: but if thou be a breaker of the law, thy circumcision is made uncircumcision. 26 Therefore if the uncircumcision keep the righteousness of the law, shall not his uncircumcision be counted for circumcision? 27 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? 28 For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh: 29 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.
It's about the heart, the law written on the heart.
The law is Spiritual. When the Holy Spirit is in us we know it is wrong to steal, kill and take the Lords name in vain.
Rom 13:8 Owe no man any thing, but to love one another: for he that loveth another hath fulfilled the law. 9 For this, Thou shalt not commit adultery, Thou shalt not kill, Thou shalt not steal, Thou shalt not bear false witness, Thou shalt not covet; and if there be any other commandment, it is briefly comprehended in this saying, namely, Thou shalt love thy neighbour as thyself. 10 Love worketh no ill to his neighbour: therefore love is the fulfilling of the law.
The 10 commandments are LOVE For God and each other expanded.
Love exisited in Eden so the principles were there.