In plain words
When you hide weapons inside this tree, no one's eye can easily see them. All its branches are full of fire. When people undertake any yajña, they put one stick of this tree above and one below and churn them. From this churning, fire comes forth. Whatever you put into fire, the fire burns it to ash. But fire protects fire alone. In this way, following Kṛṣṇa's counsel, the Pāṇḍavas hid all their weapons in that śamī tree. When the time came to take them up again, they prayed to Agni and won them back. Those very weapons, charged with the power of Agni, won them victory in the war. The day they won victory in this war is Vijayadaśamī. In the Tretā Yuga, the day Rāma too went to Laṅkā, destroyed Rāvaṇa, came back to Ayodhyā and was crowned was Vijayadaśamī as well! That is why, from that day on, people have kept the holy day of Vijayadaśamī.
‘Durgā’ means the power of Prakṛti. In this power of Prakṛti there is endless power. Saṅkalpas have no rule that they must be this or that. A man may die, but saṅkalpas do not die. Saṅkalpas are lasting. Man must accomplish such lasting saṅkalpas only on the path of Satya. These two, saṅkalpa and sādhana, are like smoke and fire. When the smoke grows, the fire dies down. When the fire grows, the smoke dies down. In the same way, of the two, the power of Prakṛti and Parāśakti, when Parāśakti grows, the power of Prakṛti dies down. And in the same way, when Parāśakti dies down, the power of Prakṛti grows. That is why, so that we lessen the power of Prakṛti and develop the principle of Parāśakti, they taught ‘Vairāgya’. The more we lessen the power of Prakṛti, the more the principle of Parāśakti grows.