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I hope this message finds you well in Christ. Though the question you ask may appear to be simple at the surface, it is a rather lengthy and complex explanation. I will do my best to synthesize the answer, but in doing so, will leave out a number of details for the sake of making this answer accessible. I am not a biblical linguistic scholar, so I defer to those who are of greater education than myself on the matter. Forgive me.
The translation that you have cited above is incorrect, on several levels; I will go from the most superficial to the deepest.
The first level is that the English translation is more accurately read as "The heart is deceitful above all things, and desperately wicked: who can know it?" This is the King James Version. The Masoretic (Hebrew) text, from which this translation and numbering is taken, says nothing of a cure or being incurable. If this was the case, that is to say, if the heart of man was said to be incurable, then there would either be no hope for us, for even Christ and His merciful forgiveness would not be a cure for our sinful hearts, or the text of the Bible would be under question to the point of being thrown out as not being divinely inspired.
The second level is that the "original" text is not, in fact, the original text. The text used for the translation is the Masoretic text. Many people who come upon the Bible would assume that the text of the Old Testament would be most accurate in the Hebrew. Unfortunately, this is not true. The Masoretic text was composed several centuries after Christ, with several lengthy modifications to the original text (this is not a matter of controversy, but rather well documented.) St. Paul and the Fathers of the Church quote extensively from the Septuagint (the divinely inspired Greek translation of the Old Testament, created a few hundred years before Christ), as this was the standard from Scripture at the time. The Greek Septuagint, being older, is in general more reliable than the Masoretic text as a result. The Masoretic text, however, is used in translations of the Bible by the Catholic Church and the vast majority of the Protestants, certainly in their published translations, and so we assume that they are dependable. A quick look into the Orthodox Study Bible, though, will show you that Jeremiah 17:9 (Masoretic) is not in fact Jeremiah 17:9 (Septuagint); it is, rather, Jeremiah 17:5 (Septuagint), which reads in the Greek as follows:
βαθεῖα ἡ καρδία παρὰ πάντα καὶ ἄνθρωπός ἐστιν καὶ τίς γνώσεται αὐτόν (The heart is deep beyond all things, and it is the man, and who can know him?).
When we examine the writings of the Fathers, this holds to be true, as this is the text that they comment on. Their commentary, then, focuses on Christ. As an example, here is an excerpt from Against Heresies by St. Irenaeus of Lyons, which includes the verse in its proper translation:
"For this reason it is said, “Who shall declare his generation?” since “he is man, and who shall recognize him?”But one to whom the Father who is in heaven has revealed him knows him, so that he understands that he who “was not born either by the will of the flesh or by the will of man”is the Son of man, that is, Christ, the Son of the living God. For I have shown from the Scriptures that no one of the children of Adam is as to everything, and absolutely, called God or named Lord. But that he is himself in his own right, beyond all people who ever lived, God, and Lord, and King eternal and the incarnate Word, proclaimed by all the prophets, the apostles and by the Spirit, may be seen by all who have attained to even a small portion of the truth. Now, the Scriptures would not have testified these things of him, if, like others, he had been a mere man. But that he had, beyond all others, in himself that pre-eminent birth that is from the most high Father, and also experienced that pre-eminent generation that is from the Virgin, the divine Scriptures do in both respects testify of him."
In summary: for a more accurate representation of the text that the Orthodox Church accepts (i.e. the Septuagint), get an Orthodox Study Bible rather than the ones printed by those in the West which use the highly modified Masoretic text. You can see how different our understanding of our relationship to God and ourselves can be.
Remember me in your fervent prayers,