Talk 2 is titled Fire because fire is the means by which the Holy Spirit manifested Himself, first to His apostles.
After the crucifixion of Jesus, His apostles, afraid that they too would be persecuted by the reigning Romans, hid in an Upper Room of one of the followers of the Lord.
On what we now call Pentecost Day, the Holy Spirit came down like fire in the Upper Room: When the day of Pentecost came, all the believers were gathered together in one place. 2 Suddenly there was a noise from the sky which sounded like a strong wind blowing, and it filled the whole house where they were sitting. 3 Then they saw what looked like tongues of fire which spread out and touched each person there. 4 They were all filled with the Holy Spirit and began to talk in other languages, as the Spirit enabled them to speak.(Acts 2:1-4 GNT, emphasis mine)
After the Holy Spirit came upon them, the 120 disciples were changed. From being cowards, hiding in the Upper Room, they became fearless. They marched out of that room ready to die for Jesus. And years later, they did. All the apostles, except John the Beloved, became martyrs.
They got out of the way.
That’s what fire does. That’s what the Spirit does. It makes us selfless. It makes us sacrifice. It makes us servants. It makes us get out of the way. It makes us get out of the way of the Holy Spirit so He can do His way of liberating the disciples—and all of us—from sin and worthlessness.