Clement the disciple of Peter spoke of the Jewish people as God's first fruits. Just as the farmer presented the first fruit of his harvest to the LORD, the Jewish people are the first fruit from among the nations.
In the days of the Temple, the farmers in Israel were obligated to give an annual tithe to Levites, then take a second tithe for festival expenses and to share with the poor. In addition to the tithes, the farmers of Israel were to offer the first fruits of their produce.
You shall take some of the first of all the produce of the ground which you bring in from your land that the LORD your God gives you, and you shall put it in a basket and go to the place where the LORD your God chooses to establish His name. (Deuteronomy 26:2)
The principle of offering first fruits means that when God prospers us, we are to show our gratitude by returning a portion to Him in the form of charitable gifts for the poor and financial support for those who do the work of the kingdom.
When writing to the Corinthians, Clement quoted a passage from Deuteronomy to demonstrate how God had divided the nations of humanity but chosen Israel as His own portion. He went on to quote an unknown source that speaks of God taking Israel out of the nations like a farmer taking the first fruits from his threshing floor. Just as the first fruits are set aside from the rest of the crop to be a holy gift to the LORD, so too Israel is set apart from the other nations to be God's holy people:
"When the Most High divided the nations ... His people Jacob became the portion of the LORD, and Israel the lot of His inheritance" (Deuteronomy 32:8-9). And in another place [it is said], "Behold, the LORD takes for Himself a nation out of the midst of the nations, just as a man takes the first fruits of his threshing floor, and from that nation shall come forth the most holy." (1 Clement 29:1-3)
We do not know where Clement found the verse about God taking Israel like "a man takes the first fruits," but it is a beautiful image. From the midst of Israel comes "the most holy," which might be a prophecy regarding the Messiah. Clement uses the verse about Israel's elect status to encourage the Gentile believers in Corinth. "God has made us partakers in the blessings of His elect" (1 Clement 29:1), he tells them, and he says, "Seeing, therefore, that we are the portion of the Holy One, let us do all those things which pertain to holiness" (1 Clement 30:1).
These comments are in keeping with the rest of Deuteronomy 26. After discussing the obligations of first fruits and tithes, Deuteronomy 26 encourages the Israelites to keep the Torah and walk in God's ways because of their exalted status as the people of God. God has set Israel above the other nations "for praise, fame and honor." In other words, we should be proud of being part of the people of God:
The LORD has today declared you to be His people, a treasured possession, as He promised you, and that you should keep all His commandments; and that He will set you high above all nations which He has made, for praise, fame, and honor; and that you shall be a consecrated people to the LORD your God, as He has spoken. (Deuteronomy 26:18-19)