We are told here to keep God's words in the midst of our heart, to not let them ever depart. And the only way that happens is if we are constantly pouring in God's words, each and every day. Not just reading them, by the way, but actually giving them attention as we evaluate our heart against God's holy standard.
We are told to keep and guard our heart with all our might. Let that sink in. We are told to keep—guard—our heart with all our might and effort, for out of it spring the issues of life.
The heart is described here as the fountainhead—hold on to that—from whence all streams of life proceed. Just as a polluted upstream water source flows downstream to infect all other waters, so too our heart must be guarded to ensure it is pure and aligned to God's standard, His holy, meek, and lowly heart.
