In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise, 14Which is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of his glory. - Ephesians 1:13-14

    The “earnest” mentioned here bears some similarity to our usage today of the phrase “earnest money” – referring to the money that is often required as a deposit when one enters into a sales contract to buy real estate.  It is money that is given to express our sincere, earnest intention to fulfill the terms we’ve agreed upon, guaranteed by the fact that legally one must forfeit their “earnest” money if they fail to follow through with the deal.  And so, here too it speaks of a guarantee – but this guarantee is from the faithful, almighty God who cannot fail.  So the saved are convinced by God the Holy Spirit of God’s gospel wherein they see all of the requirements for their salvation having been fully met by the doing and dying of their Substitute, with no contribution remaining due from their hand.  In other words, their salvation is truly to “the praise of His glory.”  And having been so convinced – having this mystery of the gospel made known unto them by the miraculous application of it to their hearts and minds by God the Holy Spirit – they have an earnest from God – a guarantee that cannot fail. 
 
    To have received the earnest of the Holy Spirit is indeed precious to these objects of God’s mercy and grace.  This work of the Spirit is one in which they are altogether passive.  And yet by God-given faith they confirm the certainty of their being sealed (of being certain for heaven’s glory), when, from the same almighty power that raised Christ from the dead, they are enabled to trust solely in Christ for the salvation of their souls, in repentance turning from the way that before seemed right to them to God’s Gospel – the gospel of their salvation.