If I say, “I will not mention Him or speak any more in His name,” His message becomes a fire burning in my heart, shut up in my bones, and I become weary of holding it in, and I cannot prevail. — Jeremiah 20:9

Jeremiah tried to hold back God's word, but he couldn't — it was a fire shut up in his bones, and he was weary of holding it in. Paul felt the same compulsion: Woe is me if I do not preach the Gospel. The love of Christ constrains us. When God's word takes hold of you, it's not a hobby — it's a fire that has to come out. Peter and John couldn't help but speak of what they'd seen and heard.