I Thessalonians 1:2-3 - 2 We give thanks to God always for you all, making mention of you in our prayers; Remembering without ceasing your work of faith, and labour of love, and patience of hope in our Lord Jesus Christ, in the sight of God and our Father;

When Paul thought of the Christians in Thessalonica, his heart filled with gratitude. Paul started the church there in less than ideal circumstances, being run out of town after only three weekends with them (Acts 17:1-10). Yet the church was strong and full of life. Paul knew that this work was beyond him and his abilities and that it was the work of God.

There were things about the Christians in Thessalonica that Paul simply could not forget. He always remembered them. What he remembered about them, made him thankful. Paul's gratitude didn't come because all the Christians in Thessalonica thought so highly of him. Later, Paul used a whole chapter defending himself and his ministry against slander and false accusations. Paul's gratitude didn't come because the Thessalonian Christians were morally impeccable. Later in the letter, Paul strongly warned them against the failings regarding sexual impurity. Paul's gratitude didn't come because the Thessalonian Christians were completely accurate in all their doctrine. He had to correct some of their wrong ideas in that area also.

Despite the problems, Paul was so grateful to God for the Thessalonians because there was an undeniable work of the Holy Spirit and a marvelous change in their lives. The three great Christian virtues were evident among them: faith, love, and hope. Here for the first time, chronologically, in Paul's writings we have this famous triad: faith, love, hope. But Paul's stress is not on these virtues alone, but rather upon what they produce.

Therefore, their faith produced work.

Their love produced labor.

Their hope produced patience, which is the long-suffering endurance needed to not only survive hard times, but to triumph through them.
Basically, Paul was saying we should pray always and without ceasing, and should pray not only for ourselves, but for others also, for our friends, and should make mention of them in our prayers. We may sometimes mention their names and should make mention of their case and condition; at least, we should have their persons and circumstances in our minds, remembering them without ceasing. Note, as there is much that we ought to be thankful for on the behalf of ourselves and our friends, so there is much occasion of constant prayer.