I know the "normal" way of looking at this verse deals with the impact the thoughts in your mind have on your life. How you think becomes how you live. That's true but it can also be said that WHO you think on will change your life as well. Of course, we want to encourage one another to think about the Lord and watch our lives be affected by those thoughts. That's true, but I'd like to suggest something else.
Think about people you know and love, especially those you would love to be saved. When you think on them you undoubtedly pray for them and you also find yourself thinking of ways to have a good witness to them. You see, when you dwell on someone in your thoughts you will find your life changes, especially after your pray earnestly for them. You begin to seek for ways to witness to them. You find your God brings their names and faces into your mind a lot and you pray even more for them. Let me illustrate with someone on my mind and heart:
His name is Manny, and he is the gas station attendant I met nearly two years ago. He was always smiling and friendly and he responded to my own smile and interest in him. Over the last couple of years I've spoken to him briefly about the Lord. He is very receptive. I spoke more directly to him about God's love for him about a month and a half ago. Last month I gave him a copy of the 199 Promises of God booklet. Last week he told me he may be going back to India, "just for a visit" but I wonder if he will be back. He's on my heat and in my thoughts. And that is affecting my life, especially every time I drive past his station, which is about twice daily! "As I think [of Manny} in my heart, so [my heart yearns for his salvation] and that makes changes in my life." My pointed paraphrase of Proverbs 23:7.
What you think on can change your life. So, WHO you think about can change you too. Whose on your mind?