The Catechism in Questions & Answers

731. How do we understand our sacrifices?

We understand our “sacrifices” to be the gifts and talents, time, and energy that are put to work in the service of God and His work.
Even the endeavour to refrain from doing something for the benefit of God’s work is a sacrifice.
Believers also feel the need to express their gratitude and love for God in concrete gifts (sacrifices), be it in the form of money or natural goods. According to Malachi 3: 10, we are to bring the “tithe” of our increase into the house of the Lord. The “tithe” can serve as a guide to the members in their offerings.