Since St Paul feels that he is obligated to fulfil the "Mystery of Christ" through the grace, enduring all difficulties for them, it is befitting that they realize the divine call by which they were called.
The servant should not be the only one who works, but every member has to play his role, or in other words, has to keep his church membership through hard work. The focus of that work is to abide in fervent love, which grants the unity of the spirit through the harmony of all the members as one body to the One Head.