The tithe is recognized as God's

The Old Testament emphasised "freewill offerings" --

The Israelites, all the men and women whose heart moved them to bring material for all the work which the Lord had commanded through Moses to be done, brought a freewill (voluntary) offering to the Lord. - Exodus 35:29

These were voluntary contributions beyond the tithe.

When the temple needed to be rebuilt, people were asked to provide freewill offerings --

Then the heads of the fathers’ households of Judah and Benjamin, and the priests and Levites, all those whose spirits God had stirred up,[a]arose to go up and rebuild the house of the Lord which is in Jerusalem.  All those who were around them encouraged them with articles of silver, with gold, with goods, with cattle, and with valuable things, in addition to all that was given as a freewill offering. - Ezra 1:5-6

 The Israelites got caught up in the thrill of giving --

And all the skilled men who were doing all the work on the sanctuary came, each one from the work which he was doing,  and they said to Moses, “The people are bringing much more than enough for the construction work which the Lord commanded us to do.”  So Moses issued a command, and it was proclaimed throughout the camp, “Let neither man nor woman do any more work for the sanctuary offering.” So the people were restrained from bringing anything more;  for the material they had was sufficient and more than enough to do all the work. - Exodus 36:4-7

The emphasis here is not on the amount of the offering or the cause for it, but the willingness of each person's heart.

Voluntary offerings were a demonstration of love, joy, and worship.  The grace of giving transformed a pack of gripers and whiners into joyful worshippers.

Moreover, because I delight in the house of my God, the [personal] treasure that I have of gold and silver, I give to the house of my God, in addition to all that I have already provided for the holy house - 1 Chronicles 29:3

Then the rulers of the fathers’ households, and leaders of the tribes of Israel, and the commanders of thousands and of hundreds, with the overseers of the king’s work, offered willingly  and gave for the service of the house of God: 5,000 talents and 10,000 darics of gold, and 10,000 talents of silver, and 18,000 talents of bronze, and 100,000 talents of iron.  Whoever had precious stones gave them to the treasury of the house of the Lord, in the care of Jehiel the Gershonite. Then the people rejoiced because they had given willingly, for with a whole and blameless heart they had offered freely to the Lord. King David also rejoiced greatly. - 1 Chronicles 29:6-9

“But who am I, and who are my people, that we should be able to offer as generously as this? For all things come from You, and from Your own hand we have given to You.  For we are [a]sojourners before You, and tenants, as all our fathers were; our days on the earth are like a shadow, and there is no hope [of remaining].  O Lord our God, all this abundance that we have prepared to build You a house for Your holy Name, it is from Your hand, and is all Your own.  I know also, my God, that You test the heart and delight in uprightness and integrity. In the uprightness of my heart I have willingly offered all these things. So now with joy I have seen Your people who are present here, make their offerings willingly and freely to You.  O Lord, God of Abraham, Isaac, and Israel, our fathers, keep forever such purposes and thoughts in the minds of Your people, and direct their hearts toward You - 1 Chronicles 29:14-18

David measured the people's loyalty to God by their willingness to freely give to God.