You could consider this as something of a Stitches in the Veil Part 2...
I honestly think that a lot of us who profess faith in Christ miss what was said here...
"...And Jesus cried out with a loud voice, and breathed His last. Then the veil of the temple was torn in two from top to bottom..."
That may be the single most important event within the text of the books of the bible. In my opinion, it IS the single most important event. It changed everything. Up until that point, the entirety of all biblical books focused on the separation of man from God and the struggles of man, in futility, to overcome that separation or to outright ignore it. Everything in the Old Testament text is a stop-gap, a history lesson, a plethora of examples of the outcome of man's separation from God.
In his fallen state, man couldn't withstand God. God was literally confined to a box so his righteousness wouldn't destroy man. Only one individual, the High Priest, was given physical access to the Holy of Holies, where God dwelt, and only once a year. Otherwise, things like the Law were given to slow the separation - a stop-gap, as I said earlier. A limited number of prophets were given access to the Holy Spirit. Otherwise, no one would've been able to hear from God. God didn't reside within man. God couldn't reside within man.
God didn't delight in the blood of rams and goats. Those things couldn't take away sin. God would only be satisfied with the ability to be within His people and live life, step by step, day by day, with them.
When a sinless Christ was crucified, and HIS blood served as the conciliation, the separation became NO MORE.
When I hear people trot out Jeremiah 17:9 as proof that the heart is wicked and deceitful...
The heart is deceitful above all things, And desperately wicked; Who can know it?
...to me it's almost a concession that they've refused to accept the sacrificial act of Christ as complete and enough. They're content to live with a veil in place between them and God, content to live without the presence of the Holy Spirit inside of their heart, their "lav", their "inner parts/inner man". It's a paradox of monumental proportion to live with the belief that your heart is deceitful and desperately wicked while claiming genuine faith in Christ. It's also a woefully poor and inexcusably irresponsible handling of scriptural passages, using no discernment, making no attempt to rightfully divide.
Jeremiah 17:9 was written to a Holy Spirit-less people in a Holy Spirit-less time. If you claim Christ, if you live under a new and better covenant, you are not a Holy Spirit-less people.
I don't pretend to know why God has done some ("most" may be a better word) of the things He's done, why He's allowed man to do so many things, why He Himself instructed men to do things that I'd never, ever want to do or consider "right" and decent. I don't know. I have to look at life here through the lens of it being little more than a grain of sand within the known universe in the context of eternity - and apply appropriate weight to it through such a lens, understanding that most of my understanding is, and will continue to be, limited in this life. But, what I do know is this...
You can't claim Christ yet still cling to Holy Spirit-less elements and aspects of old covenant belief and expect to flourish spiritually. The Spirit of God either resides in your heart (your "lav", or inner man) or it doesn't, and if you still believe your heart to be wicked and deceitful, it's time for some serious, serious examination, and time for you to either drop some dead-weight and false teachings or to just let go of your claim to faith in Christ before you hurt others with it. A heart in which the Spirit of God has taken up residence is a beautiful thing to follow - and is never to be feared.
The veil has been torn. The separation has been mediated. Why would you keep trying to hide behind it? Why would you let a religiously addicted teacher - a man - again separate you from God and sew the veil back up?
ANY man or woman who places another man or woman between you and God, or who teaches the outright (even if unspoken) denial of the Holy Spirit within the heart of a believer...is anti-Christ in every possible way.
If your heart is deceitful and desperately wicked, you need to ask yourself what your heart might be lacking. It's not like provision hasn't been made.