Summary: Writing the Romans, Paul speaks of his gratitude for them, giving some surprising reasons for being thankful.
“First, I thank my God through Jesus Christ for all of you, because your faith is proclaimed in all the world. For God is my witness, whom I serve with my spirit in the gospel of his Son, that without ceasing I mention you always in my prayers, asking that somehow by God’s will I may now at last succeed in coming to you. For I long to see you, that I may impart to you some spiritual gift to strengthen you—that is, that we may be mutually encouraged by each other’s faith, both yours and mine. I do not want you to be unaware, brothers, that I have often intended to come to you (but thus far have been prevented), in order that I may reap some harvest among you as well as among the rest of the Gentiles. I am under obligation both to Greeks and to barbarians, both to the wise and to the foolish. So I am eager to preach the gospel to you also who are in Rome.” 
“First…” I find it instructive that the Apostle’s first priority in this letter is to express gratitude. His gratitude for those to whom he writes is evident in even a cursory review of the letters he wrote to the churches and to individuals. Recall a few instances of Paul’s expressions of gratitude. Writing the Corinthians in his first letter to that congregation, Paul declared, “I give thanks to my God always for you because of the grace of God that was given you in Christ Jesus, that in every way you were enriched in him in all speech and all knowledge—even as the testimony about Christ was confirmed among you—so that you are not lacking in any gift, as you wait for the revealing of our Lord Jesus Christ, who will sustain you to the end, guiltless in the day of our Lord Jesus Christ” [1 CORINTHIANS 1:4-8].
The Ephesian encyclical reveals the Apostle’s gratitude when he writes, “Because I have heard of your faith in the Lord Jesus and your love toward all the saints, I do not cease to give thanks for you, remembering you in my prayers, that the God of our Lord Jesus Christ, the Father of glory, may give you the Spirit of wisdom and of revelation in the knowledge of him, having the eyes of your hearts enlightened, that you may know what is the hope to which he has called you, what are the riches of his glorious inheritance in the saints, and what is the immeasurable greatness of his power toward us who believe, according to the working of his great might that he worked in Christ when he raised him from the dead and seated him at his right hand in the heavenly places, far above all rule and authority and power and dominion, and above every name that is named, not only in this age but also in the one to come” [EPHESIANS 1:15-21].
The letter Paul wrote to the Christians in Philippi begins with this statement of gratitude. “I thank my God in all my remembrance of you, always in every prayer of mine for you all making my prayer with joy, because of your partnership in the gospel from the first day until now” [PHILIPPIANS 1:3-5].
Note how Paul began one other missive to a church, especially noting how the Apostle expressed gratitude for those believers. “We always thank God, the Father of our Lord Jesus Christ, when we pray for you, since we heard of your faith in Christ Jesus and of the love that you have for all the saints, because of the hope laid up for you in heaven” [COLOSSIANS 1:3-5a].
Consider one final expression of gratitude for an individual named Philemon. Paul wrote, “I thank my God always when I remember you in my prayers, because I hear of your love and of the faith that you have toward the Lord Jesus and for all the saints” [PHILEMON 4, 5].
From this brief review of the Apostle’s heart for fellow believers, it is apparent that he modelled gratitude, especially gratitude for fellow believers as they stood firm in this holy Faith. Even if nothing is ever taught in Scripture about our responsibility to be marked by thanksgiving, the example of those who preceded us should lead us to be a grateful people.
Ingratitude is the default position of the world, as Paul makes abundantly clear in a very short while. He writes, “The wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who by their unrighteousness suppress the truth. For what can be known about God is plain to them, because God has shown it to them. For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse. For although they knew God, they did not honor him as God or give thanks to him, but they became futile in their thinking, and their foolish hearts were darkened. Claiming to be wise, they became fools, and exchanged the glory of the immortal God for images resembling mortal man and birds and animals and creeping things” [ROMANS 1:18-23].