God's word is not chained

In 2 Timothy 2:8-9, Paul writes:

"8Remember Jesus Christ, raised from the dead, descended from David. This is my gospel, 9for which I am suffering even to the point of being chained like a criminal. But God's word is not chained."

 What does that last part imply? What does it mean that God's word is not chained? Paul mentions his own enchainment (a word I apparently made up, according to spell check) as suffering but maybe also as humiliating. His being chained up also means that he is restricted. Does the phrase just mean, then, that God's word is free, unrestricted? It seems the "therefore" in verse 10 applies to the fact that God's word is not chained. Maybe Paul means that God's word is free to be shared so that many can hear and "that they too may obtain the salvation that is in Christ Jesus, with eternal glory" (10). God's word is not meant to be kept up but shared. Yes, it is to be harbored deep inside us, written on our hearts, but we are also called to share it.