Family greetings aside, the kiss as a form of greeting has never been a primary part of traditional American culture, though the culture of the deep south is a bit of an exception. However, we continue to see it practiced today in parts of Europe, especially in the Mediterranean regions.
The kiss was a common form of greeting in Bible times and likely practiced similarly to today, namely, a kiss on the cheek or touching of cheeks. This is certainly the image that comes to mind when we think of the treacherous kiss of Judas Iscariot. I believe that it is Judas’ kiss that is the contrast to the holy kiss here mentioned (cf 1 Cor 16:20; 2 Cor 13:12; 1 Thes 5:26), not some idea that brethren were getting carried away in kissing one another. Our greetings are to be holy and without hypocrisy.
In Romans 16:17-20 we see warnings against the most common threat to the church then and now, false teaching. Persecution by the Jews or Romans could not destroy the church. In fact, in many cases it caused the church to grow as unbelievers witnessed the power of a converted life. As Tertullian wrote in the late second century, “the blood of the martyrs is the seed of the church.”
But false doctrine destroys the church because it causes her to be and practice something foreign to her holy calling. Thinking of Rome, the Roman Catholic Church in no way resembles the church as established in the first century. When the doctrine and practices of the church were changed, it ceased to be the Lord’s church. The church is a spiritual body, thus proper doctrine and practice are essential to its identity. False doctrines and the teachers who promote them are to be marked and avoided. So vital is pure doctrine to the life of the church that Jesus warned against false teachers in the Sermon on the Mount (Matt 7:15-20) long before He ever spoke a syllable about the church (Matt 16:13-18).
Finally, Paul closes his epistle the same way he opened it, with a call to obedience to the faith, (cf Romans 1:5, 16:25-26). In verse 25 Paul identifies the gospel and the preaching of Jesus Christ as the mean by which we are established by God. In verse 26, he said this gospel is to be preached among all nations (just like Jesus said (cf Matt 28:19; Mark 16:15) “for obedience to the faith.” Romans is a book about saving faith, but there is no saving faith apart from obedience.