Krishna stealing the gopis' clothes was significant as it was the Lord's leela to remove the ego of his devotees. The gopis were some of Lord Krishna's most ardent devotees, but even they had some ego in their hearts at times, which the Lord removed.
Krishna was a very small child at this time, around eight years of age give or take a few years. The gopis used to bathe naked in the yamuna river, the same river which people used to drink water and use for cooking. It is considered sinful to bathe naked, as it makes the water unsanitary for those who drink it and use it for cooking, so Krishna wanted to teach the Gopis a lesson by stealing their clothes. The Gopis had ego that no one would stop them from bathing naked, so Krishna in the form of a small mischievous child stole their clothes and hid them on top of the tree.
When the Gopis begged Krishna to give them back their clothes, Krishna asked them impertinent questions just like a child would. He asked them to come get the clothes themselves, and when the Gopis said they could not leave the river naked, he asked them why they were bathing naked in the first place.
Finally, the gopis' ego was broken and they realized their mistake. They plead forgiveness from Krishna and promised him never to bathe naked in the river again, thereby destroying the cleanliness of the river for everyone else.
So Krishna stealing the Gopis' clothes was not wrong. So many people today take it way out of proportion but 1) Krishna was a small child when he did it (so his relationship with the Gopis was like a mother-son) and 2) it was to teach the world a lesson about keeping the environment clean.