‘And he looked up, and saw the rich men who were casting their gifts into the treasury.'
As we see from the chiasmus of the passage Luke connects the behaviour of the Scribes towards widows' possessions with the behaviour of a godly widow towards God. Here we see one whose livelihood is swallowed up, but by her own choice because of her trust in God to provide for her. And she is also here compared with the wealthy generally. We are here reminded of Jesus' words, ‘Blessed are you poor, for yours is the Kingly Rule of God' (Luke 6:20).
In this case, which also connects up with the next passage, Jesus is possibly sitting with His disciples in the Temple courtyard not far from a group of trumpet shaped collection boxes placed in the wall of the court of the women for the purpose of receiving nominated contributions to various needs. Each box was for a different purpose which was clearly indicated on it. From there the gifts would make their way to the Temple strong room. Or it may be that they were seated near where the vow offerings were made, when the amount being offered would be openly stated to the officiating priest.
He noted how the rich men came along and ostentatiously ‘cast' their gifts into the Treasury. This ostentation linked them with the follies of the Scribes. Or it may be that they handed them over ostentatiously, making sure that all knew what they were giving. And no doubt many were watching in admiration, including possibly the disciples, who may even have commented on particularly generous gifts.