Deuteronomy 26:12 New International Version (NIV)
"When you have finished setting aside a tenth of all your produce in the third year, the year of the tithe, you shall give it to the Levite, the foreigner, the fatherless and the widow, so that they may eat in your towns and be satisfied."
From Study Notes in the NIV Life Application Study Bible: "This law is repeated from 14:28-29. The people were to give their tithe to the needy every third year. This amounts to one-third of their giving on a three-year cycle. Though we are not under this law today, the New Testament reminds us not to forget the poor. Consider giving one-third of your annual contribution to overseas ministries, or to relief for the poor, orphans, and widows."
From Study Notes in the Amplified Bible: "This is a reference to a benevolence offering given every three years (called the "tithe of the poor" by the ancient rabbis). This was in addition to the "Storehouse Tithe," brought to the sanctuary and the "Pilgrimage Tithe" used for the expenses of going to Jerusalem three times each year. Together, the Old Testament tithe amounted to a third of the total."
Tithing is our way of giving back to God a portion of what He has graciously and generously given to us.
Today, I don't think we give those second and third tithes as described in the Amplified Bible. Instead we give gifts and offerings, in addition to our tithe.
The Bible study notes explain how we should apply this verse to our lives today.
There are plenty of needy people around us. This Lenten Season we are focusing on taking care of refugees, whom the Bible clearly states we are to welcome and treat as equals. (Numbers 15:15-16)
Some people may be hesitant to step out in faith and help the needy because they themselves fear refugees or those different from them, or they fear that God will not provide for them if they give away anything they own.
I'd gently say that fear is not from God (2 Timothy 1:7); God loves a cheerful giver (2 Corinthians 9:6-7) and God promises to provide for us (Matthew 6:33).