The Truth will set you free: the context of a timeless truth

"Then you will know the truth, and the truth will set you free." (John 8:32)  The Gospel of John contains many memorable phrases, including Jesus' powerful "I am" statements.  The idea that truth is capable of making people free has penetrated Western culture to the extent that the two ideas, freedom and truth, have become inextricably linked, especially in the light of the penchant of oppressive regions for propaganda and outright lies.  For examples of the cultural triumph of a linkage between freedom and truth and conversely oppression and lies, see George Orwell's 1984 , Aldous Huxley's Brave New World , or Ray Bradbury's Fahrenheit 451.  In their own way, each of those novels is championing the ideal of Truth (with a capital T) and warning of the danger of falsehood to society.  In this they are certainly correct, for no society or government founded upon, or maintained by, lies can long endure apart from oppression.  While true, and certainly beneficial to society, this was not the reason why Jesus said that truth would set people free.  The concerns of Jesus were far more immediate, and far more specific, than championing the idea of Truth (as good and honorable a cause as that is).

By the point in the Gospel of John where Jesus says, "Then you will know the truth, and the truth will set you free."  he has already declared, "I am the bread of life" (John 6:35-48) and "I am the light of the world" (John 8:12, repeated in John 9:5) The Truth that Jesus was offering that would set those free who were willing to accept it, was that he did indeed come from the Father to warn them regarding their sins, and to offer them salvation by believing in him.  It was deliberately a very specific truth, embodied personally by Jesus, that had the power to set people free.  Free from what?  Not merely free from oppression, as wonderful as that is, but free from something far more universal and dangerous, free from slavery to sin.  As descendants of Abraham, and heirs to that Covenant, those who listened to Jesus believed that they were already free.  It was painfully true that they were not politically free, the presence of Roman troops in Jerusalem made that obvious, but they considered themselves to be morally and spiritually free as a people who endeavored to follow the Law of Moses.  They were wrong.  Jesus sought to shatter this false complacency by warning them, "If you were Abraham's children, then you would do the things Abraham did." (John 8:39)  Abraham believed God, and took steps to demonstrate that faith, even when difficult circumstances offered excuses to doubt God.  As a result, Genesis tells us, "Abraham believed the LORD, and he credited it to him as righteousness." (Genesis 15:6, quoted by Paul in Romans 4:3,20-24 and Galatians 3:6 as well as by James in James 2:23).
Knowledge of the truth is not sufficient.  Humanity is exceedingly capable of ignoring the truth, of subverting it to our own desires, and of paying lip service to it while continuing on our own path.  Without a commitment, without allowing it to change one's behavior, truth alone is powerless.  While that is true in many areas (for example: the advice you receive from your doctor; it doesn't help you if you ignore it), it is supremely true regarding our relationship with God.  There are many people who know who Jesus was (and is), who are aware of his life, death, and resurrection, but for whom those truths have no discernible impact upon their lives.  Unless truth produces transformation, it fails. 
Which brings us back to Jesus.  Belief in Jesus is the truth that will set us free from our slavery to sin.  Trust in Jesus is the beginning of the path of righteous obedience to the will of God, and hope in Jesus is what will allow us to live our lives confident that his vicarious death and resurrection are the keys to God accepting us into the kingdom of heaven.  The Truth will certainly set us free, we just need to make sure that our journey begins with a very specific truth, belief in Jesus.