In order to more fully understand the biblical doctrine of the sealing of the Holy Spirit, we look at three passages: Ezekiel 11:19, 20, II Corinthians 1:20-22, and Ephesians 3:16 - 19.
In Ezekiel, the prophet tells God's people that there will come a time when God will do something glorious. The promise is that He will change His people from the inside out. He will give them a new heart and remove the natural stony heart. This is a glorious truth in itself, but as we read, it was for a particular purpose, and that purpose was so that we may walk, keep, do and be. In response to the inner work, we are now to walk in His statutes and keep His ordinances and do them. Notice the order: the spiritual work is accomplished and the effect is obedience. This is the character of the life we have and ought to have as God's covenant people. Our changed spiritual state means that now, we have close communion with our creator. This is the first part of being sealed by the Holy Spirit.
In II Corinthians, we read that we are sealed with the earnest of our inheritance. All of His promises to us are given and performed truly and inevitably. Among humans, there are many promises that are made insincerely or are never fulfilled for a variety of reasons. But with our covenant-keeping God, all of His promises will be fulfilled. So how sure are God's promises? They are as sure as anything can possibly be. How sure is our inheritance? There is no possible way that His people will not receive it. At this point in verse 22 we also see what we have seen at every point in our study: the sealing work of the Holy Spirit is divinely initiated, performed, and completed.
In Ephesians, we see another theme that has been constant: our election, redemption, adoption, and sanctification are all for His glory. In particular, we see here 5 specific goals and purposes of our being sealed with the Holy Spirit unto His glory: 1) we are sealed unto strength in the inner man, 2) we are sealed unto communion with Christ, 3) we are sealed unto stability based upon Christ's love, 4) we are sealed unto knowledge of the extent and quality of our inheritance, 5) we are sealed unto knowledge of the surpassing love of Christ.
When we pause to meditate upon these great blessings, how can we not praise our heavenly Father and the Lord Jesus Christ for blessing us "with all spiritual blessings in heavenly places in Christ." - Ephesians 1:3