A noun in the genitive may stand in apposition to another noun in order to further define it. For example, Paul places his own name in apposition with “a servant of Christ Jesus” (Rom. 1:1). In II Corinthians 1:22 and 5:5, “the earnest [arrabon, seal, pledge, foretaste] of the Spirit” means the Holy Spirit is the pledge or down payment of salvation (cf. Eph. 1:14). Note the appositional use of the genitive in II Corinthians 5:1, where Paul calls our earthly house a tent-home. He uses this figure to contrast our present state with our future existence. According to the Apostle’s metaphor, our earthly life is temporary, like living in a tent which may be taken down at any hour. But when the terrestrial abode is no more, we have the celestial existence awaiting us, and it is everlasting. Note other genitives of apposition or definition such as “crown of life” (Rev. 2:10), “crown of righteousness” (II Tim. 4:8), and “crown of glory” (I Pet. 5:4).
Blackwelder, Boyce W. Light from the Greek New Testament (Kindle Locations 2907-2915). Reformation Publishers Prestonsburg, KY. Kindle Edition.