The Lord has sworn by his right handThe early Christian writer, Hippolytus, has in his liturgy a prayer for blessing the bread and wine of the Eucharist. And this is standard fare for the times, even for today. What many today would find curious is that he also includes a blessing for oil and a blessing for cheese and olives. What have these things to do with the Lord's Supper?
and by his mighty arm:
“I will not again give your grain
to be food for your enemies,
and foreigners shall not drink your wine
for which you have labored;
but those who garner it shall eat it
and praise the Lord,
and those who gather it shall drink it
in the courts of my sanctuary.” [Isaiah lxii, 8-9]
There are a couple things that make it difficult for us to answer that question. One is the downplayed role of Communion in Christian worship, but the other thing which makes it difficult to grasp is currency, money. Of course, the use of coinage to represent goods is hardly a modern phenomenon. Coinage predates Christianity. But what has changed since Hippolytus' time and ours is the role of currency. The way we interact economically is much more based on the exchange of currency than on the exchange of material goods. This is so much the case nowadays that many of us don't even receive paychecks anymore - the money is automatically deposited into our accounts using electricity. So we think about money and the goods for which we use it in significantly different ways. For Christians, this complicates the way we think about work and tithing - but not in any way that can't be overcome with a little reflection.
There is a temptation to think that the meaning of the bread and wine of the Lord's Supper is as simple as the bread representing Christ's body and the wine representing his blood. Of course, that is true as far as it goes - but the symbolism of the bread and the wine in the Lord's Supper is far richer than that. Isaiah lxii, 8-9 tells us that, while under judgment, Israel's bread and wine would be the plunder of gentile enemies. One reason this is a problem for the Israelites is because this wine is the work of their hands, the fruit of their labor. Isaiah says that once they are delivered from this judgment, they will be able to enjoy what they worked for. This means that in the Eucharist, the bread and wine that are given to us are representative of the fruits of our labor.
Hippolytus understands this. When we present the Communion elements to the Father, we are asking him to bless our work. And this is exactly what we are doing when we tithe. We present the Lord with a tenth of our produce (that produce which the Lord produced for us) so that he will bless the other 90%. The tithe is the sanctification of work. Because the elements of the Holy Supper also allude to work, Hippolytus finds it entirely appropriate to have them almost overlapping in the flow of Christian liturgy. Certainly bread and wine require blessing for Communion, but so do the elements of the tithe - those elements being oil and cheese and olives for Hippolytus' parishioners.
Many evangelical and non-denominational churches struggle with trying to incorporate "giving" (aka "tithing", "offerings", or "stewardship") into their services without detracting from the rhythm of their worship. Evangelicals would do well to learn from their less innovative brothers (that is, the Lutherans, Anglicans, Roman Catholics, and Orthodox). For the mainstream practice of the Christian Church to this day is to place the collection of tithes and offerings before the Eucharist. Following the collection, the offering plates are brought with the communion elements to the altar at the front of the Church to be offered to God. This is right and proper worship if Isaiah is to be believed.