And now, brothers and sisters, we want you to know about the grace that God has given the Macedonian churches. In the midst of a very severe trial, their overflowing joy and their extreme poverty welled up in rich generosity. For I testify that they gave as much as they were able, and even beyond their ability. Entirely on their own, they urgently pleaded with us for the privilege of sharing in this service to the Lord’s people. And they exceeded our expectations: They gave themselves first of all to the Lord, and then by the will of God also to us. So we urged Titus, just as he had earlier made a beginning, to bring also to completion this act of grace on your part. But since you excel in everything—in faith, in speech, in knowledge, in complete earnestness and in the love we have kindled in you—see that you also excel in this grace of giving.
I am not commanding you, but I want to test the sincerity of your love by comparing it with the earnestness of others. For you know the grace of our Lord Jesus Christ, that though he was rich, yet for your sake he became poor, so that you through his poverty might become rich. (2 Corinthians 8:1-9)
Except maybe for a proverb, a single verse of Scripture must not be read apart from it's immediate context. So we have to read 2 Corinthians 8:9 with the verses preceding it. When we do, we will see a church excelling in many areas, but Paul wants them to grow in a neglected area-- the area of giving and self-sacrifice. So Paul wrote about the wonderful brethren in Macedonia. The Macedonians were poor, yet they sacrificially gave for the needs of others. Here is a poor congregation, making themselves even poorer to for the welfare of others. Paul was persuading them to imitate the Macedonians (verses 1-8)
Here comes verse 9. Though the Macedonians were good examples of giving and self-sacrifice, the perfect and ultimate example is the sacrifice offered by the Lord Jesus. If we truly understand the grace of Jesus in Christmas, we will be gracious to others in how we serve them and in how we treat them. Perhaps the most popular portion of Scripture about the Lord's self-humbling is Philippians 2. There Paul urged his readers to have the same mindset as Christ (Phil. 2:5). Doing so will lead us away from selfishness. It will make us look to the interest of others (Phil. 2:3-4)
Theologian J. I. Packer explains the spirit of Christmas this way:
"... the Christmas spirit is the spirit of those who, like their Master, live their whole lives on the principle of making themselves poor—spending and being spent—to enrich their fellow men, giving time, trouble, care, and concern, to do good to others—and not just their own friends—in whatever way there seems need. There are not as many who show this spirit as there should be. If God in mercy revives us, one of the things he will do will be to work more of this spirit in our hearts and lives." (Knowing God; 20th anniversary edition, p.64)