Charles Spurgeon Commentary Ephesians 1:13

"in whom ye also, having heard the word of the truth, the gospel of your salvation,-- in whom, having also believed, ye were sealed with the Holy Spirit of promise," — Ephesians 1:13 (ASV)

In whom you also trusted, after you heard the word of truth, the gospel of your salvation; in whom also after that you believed, you were sealed with that holy Spirit of promise.

After faith, the Holy Spirit is given to dwell in the soul. That is the seal. It is not that the Holy Spirit brings a seal with him. He is the seal. Where he dwells, he is the seal of God's love to that person.