Earnest

The Spirit is the earnest of the believer's destined inheritance
(2 Cor. 1:22; 5:5; Eph. 1:14). The word thus rendered is the
same as that rendered "pledge" in Gen. 38:17-20; "indeed, the
Hebrew word has simply passed into the Greek and Latin
languages, probably through commercial dealings with the
Phoenicians, the great trading people of ancient days.
Originally it meant no more than a pledge; but in common usage
it came to denote that particular kind of pledge which is a part
of the full price of an article paid in advance; and as it is
joined with the figure of a seal when applied to the Spirit, it
seems to be used by Paul in this specific sense." The Spirit's
gracious presence and working in believers is a foretaste to
them of the blessedness of heaven. God is graciously pleased to
give not only pledges but foretastes of future blessedness.