The Mosaic code required the Israelites to consecrate the firstfruits of their harvest to God. These were to be brought to the temple and given to the priests for their support. Thus, the Lord’s people are spoken of as “the firstfruits,” meaning those dedicated to him and his service (D&C 88:98).
In a more specific sense, as in the present verse, Christ is spoken of as “the firstfruits,” thus conveying the idea that the fruits or labors of his life were fully consecrated to his Father.