3 John 1:3-4 meaning

John tells the believers receiving this letter how he came to know of their spiritual vitality. Brethren came and testified that they were walking in truth. This is how to have our soul prosper (verse 2). Embracing current reality enriches the soul. The Bible and the Spirit lead us to see what is real and true. John received a testimony from brethren who came to where John was and testified that the believers meeting at the house of Gaius were walking in truth. Why did these messengers come? Likely not to make that report only, but also to report on trouble in the church. John makes clear at the end of the letter that he expects to be there in person very soon. But the matter of bad leadership brought to him by the brethren who came and testified to John had sufficient urgency to require an immediate written response, likely sent back with the brethren who came and testified to John.