"She has given from her poverty"(Luke 21:4.
Jesus' praise for the poor widow who put her last two coins into the Temple treasury reveals a pattern he lived himself and asks his disciples to emulate. Give from your want, your lack, even your emptiness, and your gift will be multiplied.
When Jesus sends out the disciples two by two to preach the kingdom of God, they go without money, shoes, even a change of clothes. Their emptiness will invite others to open their doors to strangers, thus receiving God's blessing. When hungry crowds press in on Jesus in the wilderness, he tells his disciples, who have nothing, to give them what little they have anyway. Everyone experiences an overflowing abundance. The pattern is set, paradoxical and always risky. If you want the gift, let go of what you already have.
Jesus himself was the self-emptying gift of God, the divine kenosis. He in turn emptied himself into the world in an outpouring of selfless love from the cross. In John's Gospel, Jesus' death is also his lifting up -- resurrection, ascension -- and his final breath is also Pentecost. The Spirit is given in this last breath and the church is born from his pierced side in an outpouring of blood (Eucharist) and water (baptism). It is a sign so rich with meaning only eyes opened by faith can see (believe) it.
The poor widow, by definition bereft of all protection and support, proclaimed God's kenosis by her act of total generosity. Others gave more, but from their surplus, so it cost them little and, perhaps, was deductible at tax time. Astute and practical, these other Temple donors departed feeling they have done their charitable duty to God, but they missed altogether an invitation to enter God's kingdom.