What is the meaning of the Prophet's saying, peace and blessings be upon him, in the Hadith of the captives of Badr: "...you are a burden..."?

The meaning of "أَنْتُمْ عَالَةٌ" (antum 'aalah) is "you are poor."

This phrase appeared in the story of the prisoners of Badr, when the Prophet, peace and blessings be upon him, consulted his Companions about their fate. Abu Bakr suggested keeping and admonishing them, while Umar suggested striking their necks, and Abdullah ibn Rawahah suggested burning them. The Prophet, peace and blessings be upon him, then broke his silence and said, "Indeed, Allah softens the hearts of men in His cause until they are softer than milk, and indeed, Allah hardens the hearts of men in His cause until they are harder than stones." He likened Abu Bakr to Ibrahim and Isa in compassion, and Umar to Musa and Nuh in severity. Then he said, "أَنْتُمْ عَالَةٌ; فَلَا يَنْفَلِتَنَّ أَحَدٌ مِنْهُمْ إِلَّا بِفِدَاءٍ أَوْ ضَرْبَةِ عُنُقٍ" ("You are poor; so let no one among them escape except by ransom or a strike to the neck"). It was mentioned that they were 'aalah (poor) due to their poverty at the beginning of the Islamic state.