Ephesians 1:13 ...you were sealed with the Holy Spirit of the promise, (14) ...unto the redemption of the acquired possession, to the praise of His glory. 2 Corinthians 3:18 But we all with unveiled face... are being transformed into the same image from glory to glory, even as from the Lord Spirit.
Every seal has an image. The Spirit as the seal of God upon you bears the image of God and the expression of God. The word “unto” in verse 14 means a great deal.
We are God's acquired possession, and the redemption of the acquired possession is the redemption, the transfiguration, of our body [at the time of rapture]. By this we see that the seal of the Spirit is not a once-for-all matter. Rather, the sealing is still taking place.
The seal was put in our spirit when we believed. It begins in our spirit and it is spreading into our mind, emotion, and will. For example, if we begin to argue with others over teachings, it will become apparent that our mind does not bear the image of God.
Furthermore, in arguing over doctrine you may become angry. This indicates that the sealing of the Spirit has not yet spread into your emotion. Eventually, you may become so angry with a brother over doctrine that you decide to no longer fellowship with him.
You exercise your strong will to terminate the fellowship with this brother. Showing that in your will there is no evidence of the sealing of the Spirit. Therefore, we need to have the assurance that the sealing of the Spirit is spreading in our being.
When our whole being has been sealed, we shall be ready for the redemption of the body.