Luke 21:3, "And he said…This poor widow has given more than all of them: for they gave out of their wealth, having more than enough for themselves: but she, even out of her need, has put in all her living."?
In Luke 20:45-47, Jesus is warning the disciples to not have the proud spirit of the scribes. He says, "Beware of the scribes, who like…chief seats in the synagogues, and places of honor… who devour widows' houses, and for appearance's sake offer long prayers; these will receive greater condemnation." Through this context, Jesus is contrasting arrogant, show-off people with the humble widow who quietly gave all she had.
The account of this event, also recorded in Mark 12:41-44, does not identify the context of the offering. Historically, there were 13 chests in the temple into which people could donate money for different purposes: offerings for specific sins, offerings to help with temple maintenance and sacrifices, offerings to help the poor.
For example, 2 Kings 12:9 and 2 Chronicles 24 informs us the temple of the Lord was in disrepair. Jehoiada the priest put a chest with a hole in the lid next to the altar for offerings to repair the temple. The people brought what their heart prompted them to bring and put it in the chest. The work was then completed.
In Nehemiah 13:13, treasurers were appointed to distribute to the Levites for their service in the temple. (Please recall the Levites had no inheritance in the land.) The food and money put into this treasury came from a voluntary system in Israel where people brought a tenth of their corn, wine, and oil to support the Levites. Offerings also came from the spoils of war, as is shown by the silver, gold, brass, and iron from Jericho being put into the treasury in Joshua 6:24, and also what David had stored up for the building of the temple in 1 Kings 7:51.
However, the point Jesus was making was the woman's generosity. It wasn't what the money was used for, but the heart condition of the giver. She was giving to the Lord from her heart, and was focusing on God's will and work and not her own earthly will and work.
How different this is from the prosperity gospel that some preach. If we are living according to God's word, we choose to suffer earthly losses so that God will be ultimately glorified. The Lord Jesus was homeless, “…Foxes have holes and birds of the air have nests, but the Son of Man has no place to lay his head,” Matthew 8:20. Additionally, Christians are to follow His example of not seeking earthly pleasure, “Then said Jesus unto his disciples, If any man will come after me, let him deny himself, and take up his cross, and follow me,” Matthew 16:24. As the apostle Paul says in Romans 8:18, "For I consider that the sufferings of this present time are not worthy to be compared with the glory that is to be revealed to us."