Jesus spent the afternoon of the day of His resurrection walking and talking with two of His disciples. "He interpreted for them every passage of Scripture which referred to Him" (Lk 24:27). As Jesus taught His disciples the Scriptures, their hearts began to burn within them (Lk 24:32). This sensation indicated that their hearts were being purified. Thus, Jesus spent the afternoon of His resurrection day purifying hearts through teaching the Bible (see Eph 5:26). Jesus is doing the same thing on this resurrection day (see Heb 13:8).
If we let Jesus purify our hearts, our words become powerful, healing, and life-changing, for we speak out of the abundance of our hearts (Lk 6:45). For instance, before Peter's heart was purified by the fire of the Holy Spirit, his words were often prideful and powerless. After Pentecost, however, Peter's words were "spirit and life" (see Jn 6:63). He led 3,000 people to Christ on the first Christian Pentecost (Acts 2:14, 41). He told a man who was lame from birth to walk and the man was healed (Acts 3:6ff). The Holy Spirit fell upon the household of Cornelius when Peter started to preach to them (Acts 10:44).
When we speak out of a pure heart, we speak out of God's heart. Then we speak with the power of God's word. "Blessed are the pure of heart, for they shall see God" (Mt 5:8, our transl.).