'Voluntarily' in the Bible

Then Joash said to the priests, “All the dedicated money brought to the Lord’s temple, census money, money from vows, and all money voluntarily given for the Lord’s temple,

‘Then this shall be the sign [of these things] to you [Hezekiah]: this year you will eat what grows of itself, in the second year what springs up voluntarily, and in the third year sow and reap, plant vineyards, and eat their fruit.