Commentators believe these brethren stopped working due to misunderstanding the nearness of Christ's return. Nonetheless, they were breaking the pattern of conduct set by Christ Himself and taught by the apostles. Jesus worked right up until He was crucified. Paul calls their conduct unacceptable and serious enough that those brethren who were patiently working should withdraw from those who quit (II Thessalonians 3:6)!
This example contains a practical truth about work that is not mentioned but is helpful to understand. Costs are tied to work, whether it is for the Lord or an employer, and not the least of these is sacrifice on the part of the laborer. Jesus teaches this in Matthew 16:24: “Then Jesus said to His disciples, 'If anyone desires to come after Me, let him deny himself, and take up his cross, and follow Me.'”
To be an active, producing Christian, Jesus says that, in laboring under and with Him, we must deny ourselves and then take up, carry, or bear up under whatever the cost may be. Thus, sacrifices are involved in Christian responsibilities, as well as in our day-to-day job, but Jesus particularly aims this comment about Christian works at His followers. Denying ourselves is required because the carnal nature is always present and invariably desires to take it easy and do the wrong things through ingrained habit. However, if we give in to this, profit in Christian life diminishes.
This we do not want because, without denying ourselves, life is guaranteed to be a failure. Recall how concerned Solomon was about profit. Life will be profitable if we do the right things, but sometimes, to do so we must literally will ourselves to do what is required. Sacrificing is the only means to accomplish what needs to be done.