I started to think in threes.

As I prayed, slowly the mind of God started to be revealed. I started to think in threes. It was no great deal. No flashing lights from heaven. No sudden inspiration. Just a slow development of a thought, until I realized that God in his wisdom had given the key. If only Christians would get together in groups of three to pray for their non-Christian neighbours and friends, wouldn’t they then become the answer to their own prayers, and God would give them opportunities to share their faith at a very natural and ordinary level? And surely if they were able to share their faith with their non-Christian neighbours, and they came to Christ, then that group of three would be the first point of reference for those new Christians. That would fit in with Eddie Gibb’s scheme, I thought. He wanted to see nurture groups established in the aftermath of the main Billy Graham meetings. What better way to nurture them than to to have a group of three turning from a prayer group into a nurture group.

What does the sentence in red mean?