First, we would have to memorize all of the 613 laws that applied, or might apply in the future, to our societal position. Then we would have to remember all these laws without fail 100% of the time.
Ignorance was not an excuse for breaking one of the laws or commandments. Leviticus chapters 4, 5, & 6 deal specifically with the sacrifices which those who unknowingly broke a law were to make once they found out that they had violated it. Until then their sin was counted against them, even though they had not even realized that they had committed a sin.
There is also a problem with the belief that we can keep The Ten Commandments while rejecting the other laws and commandments and still claim to be keeping the Mosaic Law. In Mark 12:28-31, Jesus himself was asked which commandment was the most important. Jesus' reply did not even include any of The Ten Commandments. Instead, he told them that there were two other commandments which were to be recognized as most important. 'You will love the Lord your God' (Deuteronomy 6:4) and 'You will love your neighbor as yourself' (Leviticus 19:18b).
So what does this mean? It means that even Jesus Christ saw the 613 laws as a set. His answer makes it clear that there are, in all probability, other laws and commandments somewhere in that set of 613 that he also considers as even more important than The Ten Commandments. So to say that we will follow The Ten Commandments while rejecting the other laws and commandments found in Torah obviously does not conform to Jesus' own perspective concerning the laws of Torah.
Also, his words concerning the practical aid we are to show to those in need mirror another part of the set of 613 laws, namely, remembering the poor. In Matthew 25:31-46, he orders that we feed the hungry, clothe the naked, comfort the sick, and visit those in prison. We are to be the means of alleviating their suffering, just as the Hebrews of the OT who were wealthier were to see themselves as the means of alleviating the suffering of others in Israel.
To jump between the Old Testament Laws and the New Testament Laws as if we were at a salad bar profits us in no way. The 613 laws of Torah are a set, and are to be respected as one of the earliest civilized foundations of a society. But their purpose was only to turn what was little more than a ragtag mob into a cohesive unit, able to live safely among one another and defend themselves against their enemies.
We Christians have a different set of laws and commandments. But these laws and commandments are to be seen as the outgrowth of our salvation, rather than a mean of strengthening a certain nation. We have Jesus' teachings in the gospels as to what we are to do, and refrain from doing. We have the epistles, which teach us what our mindset is to be (a good example is Galatians 5:16-26). And we are to understand that as a measure of our gratitude to God for what he has already given us, namely, eternal life, it is only fair that we endeavor to have our words and actions show this gratitude through our willingness to do as Christ has instructed.
What is new is the depth of perception that Yeshua is presenting.. not just adultery but even lust is included... not just murder but even evil thoughts are included...
1 John 2:7
Brethren, I write no new commandment unto you, but an old commandment which ye had from the beginning. The old commandment is the word which ye have heard from the beginning.
2 John 1:4 I rejoiced greatly that I found of thy children walking in truth, as we have received a commandment from the Father. 5And now I beseech thee, lady, not as though I wrote a new commandment unto thee, but that which we had from the beginning, that we love one another. 6And this is love, that we walk after his commandments. This is the commandment, That, as ye have heard from the beginning, ye should walk in it.
Deuteronomy 7:9
Know therefore that the LORD thy God, he is God, the faithful God, which keepeth covenant and mercy with them that love him and keep his commandments to a thousand generations;
Love and Keep are tied together...
Exodus 20:6
And shewing mercy unto thousands of them that l
ove me, and keep my commandments.
Deuteronomy 5:10
And shewing mercy unto thousands of them that love me and keep my commandments.
Deuteronomy 7:9
Know therefore that the LORD thy God, he is God, the faithful God, which keepeth covenant and mercy with them that love him and keep his commandments to a thousand generations;
Deuteronomy 11:1
Therefore thou shalt love the LORD thy God, and keep his charge, and his statutes, and his judgments, and his commandments, alway.
Deuteronomy 11:22
For if ye shall diligently keep all these commandments which I command you, to do them, to love the LORD your God, to walk in all his ways, and to cleave unto him;
John 14:15
If ye love me, keep my commandments.
John 14:21
He that hath my commandments, and keepeth them, he it is that loveth me: and he that loveth me shall be loved of my Father, and I will love him, and will manifest myself to him.
John 15:10
If ye keep my commandments, ye shall abide in my love; even as I have kept my Father's commandments, and abide in his love.
1 John 5:2
By this we know that we love the children of God, when we love God, and keep his commandments.
1 John 5:3
For this is the love of God, that we keep his commandments: and his commandments are not grievous.