I have heard countless people use this verse to send the message that people should guard their hearts in romantic relationships, putting a "hold onto your heart for the right person to come along" spin onto the verse. While that may be a component to the verse (in my opinion a far fetched one) I don't think its the only one, or even the main one. I think that the verse has to do with what Paul talks about in Romans 10:10.
Paul says this in Romans 10:10 "For it is with your heart that you believe and are justified, and it is with your mouth that you confess and are saved"
So why should you guard your heart? it is because it is with your heart that you believe and are justified (Romans 10:10) Your heart is a key component to your faith and to your salvation.
Which leads me to say...guarding your heart does not mean smothering, stifling, ignoring, or otherwise killing your heart and what you feel there. It is the wellspring of LIFE! it needs to be alive and AWAKE! Guarding your heart means keeping things you know are bad for it away from it. Keeping things that pull you away from God out of your heart, whatever that may be. Guard your heart does NOT mean don't extend love to people. You should love everyone! "God is love and whoever lives in love lives in God and God in him (1 John 4:16)" You need your heart to be free of worldly garbage and full of God so that it can be the wellspring of life.
What is said right after the guard your heart verse?
"Put away perversity from your mouth; keep corrupt talk from your lips" (Proverbs 4:24)
Why?
-- These two components, heart and mouth, go hand in hand (ha!)
The second part of Romans 10:10, as said before, states that, "it is with your mouth that you confess and are saved"
The state of your mouth and the words that come out of it also reflect what is in your heart, as Jesus himself says in Matthew 12:34 "You brood of vipers! How can you who are evil say anything good? For out of the overflow of the heart the mouth speaks."
It is as if the two components, heart and mouth, work complimentary with each other. The heart being a little more important because it is the source for and behind the words of the mouth.
So why are these two things so important? Why should we guard them and keep them from perverse things? Paul has an answer for that as well:
"If you confess with your mouth 'Jesus is Lord' and believe in your heart that God raised him from the dead you will be saved. For it is with your heart that you believe and are justified and it is with your mouth that you confess and are saved"(Romans 10:9-10)
As Proverbs says, your heart is the wellspring, the fountain, of LIFE! Eternal life through belief in Jesus Christ.
