In whom you also trusted, after that you heard the word of truth, the gospel of your salvation: in whom also after that you believed…
The sealing of the Spirit is, His giving a sure and certain testimony to the reality of that work of grace He hath wrought in our souls, and to our interest in Christ and the promises, thereby satisfying our fears and doubts about our estate and condition. Every matter of weight and concernment is to be proved by two sufficient witnesses (Deuteronomy 19:15). Our sincerity and interest in Christ are matters of the deepest concernment to us in all the world, and therefore need a further witness to confirm and clear them than that of our own spirits (Romans 8:16). Three things concur to the Spirit's sealing work. He sanctifies the soul; He irradiates and clears that work of sanctification; He enables it thereby to apply promises. The first is His material or objective seal; the latter His formal sealing. None but the Spirit of God can clear and confirm our title to Christ, for He only searcheth the deep things of God (1 Corinthians 2:10); and it is His office (Romans 8:16) to witness with our spirits. This seal or witness of the Spirit must needs be true and certain, because omniscience and truth are His essential properties. He is Omniscient (1 Corinthians 2:10), and therefore cannot be deceived Himself. He is the Spirit of truth (John 14:17), and therefore cannot deceive us; so that His testimony is more infallible and satisfactory than a voice from heaven (2 Peter 1:19). If an angel should appear, and tell us Christ had said to him, Go and tell such a man that I love him, that I shed My blood for him, and will save him, it could never give that repose and satisfaction to the mind as the internal witness or seal of the Spirit doth; for that may be a delusion, but this cannot. The witness of our own heart may amount to a strong probability, but the witness of the Spirit is demonstration (1 John 4:24). So that as it is the design and work of Satan to cast in doubts and fears into gracious hearts, to perplex and entangle them, so, oppositely, it is the work of the Spirit to clear and settle the sanctified soul, and fill it with peace and joy in believing (John 16:7; Romans 14:17). In sealing He both attests the doctrine or object of faith, and the infused habit or grace of faith. Of the former He saith, This is My word, of the latter, this is My work; and His seal or testimony is evermore agreeable to the written word (Isaiah 8:20). So that what He speaks in our hearts, and what He saith in the Scripture, are evermore concordant and harmonious testimonies. To conclude: In sealing the believer He doth not make use of an audible voice, nor the ministry of angels, nor immediate and extraordinary revelations, but He makes use of His own graces implanted in our hearts, and His own promises written in the Scriptures; and in this method He usually brings the doubting, trembling heart of a believer to rest and comfort.
Parallel VersesKJV: 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,