2 Cor.1:21 – Now He who establishes us with you in Christ and has anointed us is God, who also has sealed us and given us the Spirit in our hearts as a guarantee.
Paul uses an incredibly descriptive word translated “guarantee” in our translation (arrhabon). This was the word for engagement ring. What is Paul trying to say? He is saying that the Holy Spirit is the promise from God concerning our eternal inheritance. Just as a future groom gives an engagement ring to his future bride giving her his promise of a life together until death separated them, the Lord gives us the arrhabon as a taste of our life together for eternity. The Holy Spirit Himself is the guarantee giving us a sense of the greatness of life forever with Him, let me say that again, the Holy Spirit is the engagement ring. Here is what the ESV Expository Commentary says about this verse.
“But the Spirit is not just a transforming power. The presence of the Spirit signifies something far greater and broader: the dawning of the new age. In referring to the Spirit as a “guarantee” or “down payment”—that is, an earnest, a pledge, an initial deposit—Paul is tapping into the language and categories of inaugurated eschatology. The Spirit is not only a down payment now in the individual believer’s life, ensuring final salvation hereafter. More fundamentally, the gift of the Spirit is the preeminent sign of the dawning eschaton (Joel 2:28–32), signaling the descent of the latter days. To receive the Spirit as a down payment signals not only a what regarding a Christian’s renewed existence but also a when regarding the time in history in which one is now located. We will see the reality of the dawning new age throughout 2 Corinthians.”
So the very existence of the work of the Holy Spirit in our modern world is extremely prophetic. Peter preached this on the Day of Pentecost. “In the last days” Peter said, “I will pour out my Spirit on all people”. The presence of the Spirit upon us gives us a taste of our eternal inheritance and it is a word to the world that the end of this age is here, receive the Holy Spirit. The Holy Spirit is being poured out all over the world, this is God’s declaration, the end of all things is near.