We have the disease because we are born into an infected world. No one escapes the effects of sin. As proof ... everyone dies. Death is the result of sin being in the world.
The cure involves cooperating with God as we go through our life, being cured by being made more like Christ, transformed by the grace of God as we cooperate with Him, which involves how we live our lives. Either we cooperate with Him, and are changed, or we go our own way, and are not.
Salvation is not just a moment in time conversion, and then going your own way to ignore God for the rest of your life. (I'm not saying that you are saying this.) Such a "faith" would not be living, saving faith, but a dead faith that James talked about - faith without works is dead.
Our "medicine" is taken throughout our lives, continually. In this way, we continue to choose. But there is no middle, neutral position. Either we take our medicine, walk with Christ, growing closer to God, or we do not, and grow sicker in sin, further from God, day by day. And for many/most people, it's at least some mixture of both. But the Christian strives to move closer to God and cooperate with His grace, even if we fail in certain things or times. We simply repent, and get up and keep going.