The first detail that Paul mentions about the church in Rome in this verse is its public witness – he says that their ‘obedience is known to all’. I suppose he means by obedience their adherence to the gospel and its requirements. This was a good testimony to have, and it brought joy to the heart of Paul even although he had not yet been to Rome to see for himself what the church was like.
Yet in a sense, he went on to say to them that while their past and present was good, they had to ensure that the future retained that standard, and there was only one way to ensure that would be the case. He repeats therefore his instruction to have nothing to do with wrong doctrines. Such a choice is the path of wisdom, says Paul.
There are circumstances in life in which it is not good to be unaware of various factors. It is essential that we know the Highway Code when we decide to drive a vehicle, both for our own benefit and for the good of others. The fact that some people ignore it is not a reason for us to imitate them. On the other hand, there are other aspects of life in which it is to our benefit to know nothing about them, and the one that Paul stresses is that we should avoid any influence that would cause us to move away from the requirements of God.
There are so many voices around today suggesting a variety of things, but the best response to all of them is to know the gospel and its requirements, and stick to them in a prayerful way, depending on the Lord for his protection. If we do that, we will remain a healthy church that pleases God.