No one can keep the law, and no one has ever been able to keep the law, with the one exception of Christ, of whom the law is a prophecy. As is written:
“And all Israel transgressed your law and turned aside so as not to
listen to your voice, and so the curse and the oath which was written
in the law of Moses, the servant of God, has been poured out upon us,
because we have sinned against him." Dan. 9.11
"Egypt, Judah, and Edom, and the Ammonites, and Moab, and all those
who are trimmed to the side, those who live in the desert, for all the
nations are uncircumcised, and all the house of Israel are
uncircumcised of heart.” Jer 9.26
And also Jer 17.9
The heart is deceitful more than anything else, and it is disastrous.
Who can understand it?
Jesus, speaking to the Pharisees:
‘Did not Moses give you the law, and yet none of you keepeth the law?
Why go ye about to kill me?’
The only possible way to keep the law today, or in the day of Moses, or in the day the letter of Galatians was written, is by faith in Christ, relying on his obedience of the law rather than your own efforts.
All of us have wandered about like sheep; we each have turned to his
own way; and Yahweh let fall on him the iniquity of us all.
He was oppressed and afflicted, yet he did not open his mouth; he was
brought like a lamb to the slaughter, and like a sheep is dumb before
its shearers, so he did not open his mouth.
Only Christ has kept the law and only Christ keeps the law today.
Return, we beseech thee, O God of hosts: look down from heaven, and
behold, and visit this vine: and the vineyard which thy right hand
hath planted, and the branch that thou madest strong for thyself. It
is burnt with fire, it is cut down: they perish at the rebuke of thy
countenance. Let thy hand be upon the man of thy right hand, upon the
son of man whom thou madest strong for thyself. So will not we go back
from thee: quicken us, and we will call upon thy name. Turn us again,
O LORD God of hosts, cause thy face to shine, and we shall be saved. Psalm 80.14-19
In that sense, all Christians who are crucified with Christ and are "quickened" with Christ born in them keep the law perfectly as well, because Christ is the prophecy and fulfillment of the law, but this is the only possible way to keep the law, and this has always been the only possible way to keep the law.
The idea that there is a middle category of "observant" people who take a handful of the commandments (skipping the animal sacrifices as the Temple was destroyed, and half the feasts, and the sabbath years and jubilee years because of loopholes) and do their best, and that such behavior is acceptable for keeping the law from their own contrivances and the little sparks they have kindled -- this not treated kindly in either the law or the prophets, as the law can only ever be kept by faith in the Holy One, not by our own efforts:
But the word of the LORD was unto them
precept upon precept, precept upon precept,
line upon line, line upon line,
here a little, and there a little:
that they might go, and fall backward,
and be broken, and snared, and taken. Is. 28.13
Who is among you that feareth the LORD, that obeyeth the voice of his
servant, that walketh in darkness and hath no light? let him trust in
the name of the LORD, and stay upon his God. Behold, all ye that
kindle a fire, that compass yourselves about with sparks: walk in the
light of your fire, and in the sparks that ye have kindled. This shall
ye have of my hand, ye shall lie down in sorrow. Isa 50.11