Many people think that religion is a private matter, and that one faith is equal to all others.  That is not the Bible's view of faith in Jesus Christ.  It is true that believing the gospel is personal - everybody has a personal responsibility to respond to the gospel message and to put their trust in Jesus; but it can never be kept entirely private (Acts 4:20).  The reason is that those who commit themselves to Christ receive God the Holy Spirit into themselves, and He starts to change them from the inside (Romans 8:9).

There should always be external evidence of an internal commitment to Jesus Christ.  That evidence will be talked about and the news will spread.  Paul had never been to the church in Rome, but he had heard about the faith of the believers from other people who had met them.  They said that the faith of the Christians in Rome had been truly life-changing.  That sort of evidence was the reason why the gospel spread through the Roman Empire despite persecution.  It should be the normal testimony of every believer.

That is why Paul thanked God for them.  But why thank God through Jesus Christ?  New Christians often ask that question.  The logic is straightforward.  God is totally holy and righteous, and we are not.  He will not hear the prayers of sinful people (all of us, including the Apostle Paul) because of our sin (Isaiah 59:2).  But Jesus has taken all our sins to His cross, making Himself personally responsible for them, so that all who trust in Him might be made righteous before God (2 Corinthians 5:21).  Jesus is the only mediator between us and God (1 Timothy 2:5).

If you were charged with the 'crime' of being a follower of Jesus Christ, would there be enough evidence to convict you?  It is a good question.  If you have come to Jesus in repentance and faith, welcoming His Holy Spirit, then the old slavery to sin should be broken and a new appetite for holiness should have arrived.  Those internal changes will affect how you deal with people, money and work.  Instead of selfish ambition, love will desire the best for others; instead of intolerance, patience and kindness will be evidence of the Holy Spirit's work (Galatians 5:22-23).  So, ask for His help to follow Jesus, and let others see that Jesus Christ really is your Lord (1 Corinthians 12:3).