The moment you can say and feel, "I am the soul," and meditate on this truth, your soul's infinite purity will enter into your heart. Then, from the heart, the infinite purity will enter into your mind. When you can truly feel that you are only the soul, the soul will purify your mind.
“Prayer for peace in my heart” is partially based on Ephesians 2:13-18 which speaks about how Jesus is our only true peace. He makes peace between you and God by ending all conflict and hostility. But beyond just an end to disagreement, true peace is a unified heart. Pray for peace in your heart and God will give it to you.