It is impossible to obey the Law. Jesus observed the Law perfectly so we don't have to try to keep it.
No Scripture has been given to support this objection when it has been presented.
There are several problems with this objection, the first being the inherent assumption that it is impossible to obey the Law.
Both Moses and Paul agree this is not true...
"For this commandment which I command you today is not too difficult for you, nor is it out of reach. It is not in heaven, that you should say, 'Who will go up to heaven for us to get it for us and make us hear it, that we may observe it?' Nor is it beyond the sea, that you should say, 'Who will cross the sea for us to get it for us and make us hear it, that we may observe it?' But the word is very near you, in your mouth and in your heart, that you may observe it." (Deuteronomy 30:11-14)
Paul states that the faith he is preaching is the exact same faith that Moses proclaimed above:
But the righteousness based on faith speaks as follows: "DO NOT SAY IN YOUR HEART, 'WHO WILL ASCEND INTO HEAVEN?' (that is, to bring Christ down), or 'WHO WILL DESCEND INTO THE ABYSS?' (that is, to bring Christ up from the dead). But what does it say? "THE WORD IS NEAR YOU, IN YOUR MOUTH AND IN YOUR HEART"--that is, the word of faith which we are preaching... (Romans 10:5-8)
So the commandments are not too difficult for us to obey.
Required for Salvation?
The second problem with this claim is the implied assumption that obeying the Law is required for salvation.
Christ's work on the cross accomplished our salvation... that is true.
If Christ had disobeyed the Law at any point, He would have sinned and invalidated His Messiahship... that also is true.
However, it is not true that our obedience to the Law is required for our salvation. That's not the purpose of the Law!
If we obey (or attempt to obey) the Law, our obedience should be as a result of our salvation in Christ... not an attempt to obtain salvation apart from Him.
Linking Christ's work (salvation) with our work (obedience to the Law) is clearly an error.
The third problem with this claim is the horrendous consequence that would result if it were true.
If we disregard the Law because "Jesus did it for us" then we actively place ourselves into the group to whom Messiah says:
And then I will declare to them, 'I never knew you; DEPART FROM ME, YOU WHO PRACTICE LAWLESSNESS.' (Matthew 7:23)
Anyone who espouses this claim must recognize that they are saying they are now free to steal, murder, lie, cheat, and commit adultery (all prohibited by God's Law). And yet Messiah says:
If you love Me, you will keep My commandments. (John 14:15)
Messiah tells us the consequences of disregarding the Law and teaching others to disregard it as well:
Whoever then annuls one of the least of these commandments, and teaches others to do the same, shall be called least in the kingdom of heaven; but whoever keeps and teaches them, he shall be called great in the kingdom of heaven. (Matthew 5:19)
Clearly this claim is inconsistent with the life and teachings of Christ.