"Do not be deceived, God is not mocked; for whatever a man sows, that he will also reap," Galatians 6:7. If no one interferes with God's law, the person refusing to work will have bad consequences. The natural consequences will motivate that person to work.
Many good-hearted Christians think it’s loving to rescue someone from problems. But they are breaking God’s law of sowing and reaping! Rescuing gets old fast. The rescuer tries to change the lazy one, but the lazy one does not change. He's living the "good life" without working.
When Adam and Eve were expelled from the garden, God could have made life easier for them. But then mankind would not have experienced the results of sin. They would not have appreciated righteousness. This is why God is permitting evil! We are directly experiencing the consequences of sin and we don't like it.
In the resurrection, mankind will learn righteousness (Jeremiah 31:33, 34), and because they experienced consequences of sin, they will be willing to change. They will say, "I'll try God's way."
So, is laziness a sin? Yes. 2 Thessalonians 3:10 (NKJV), "If anyone will not work, neither shall he eat." But if you are planning to try to convict a lazy person of his sins by quoting this scripture – be prepared to be frustrated. No one has the power to change another person. However, if you step aside and let the lazy person experience the consequences of his behaviors, he will choose to work by himself!