2 Corinthians 1:21

Now he that establisheth us with you in Christ, and anointed us, is God; who also sealed us, and gave us the earnest of the Spirit in our hearts.

Three things in these verses - (1) the anointing; (2) the sealing; and (3) the giving of the earnest are all references to one action, that of conversion - by which the believer is united with Christ "in Christ." This action, as evident on Pentecost, was a compound act of obedience: believing, repenting, being baptized, receiving the gift of the Holy Spirit. After discussing various theories on this, Hughes stated that:

It is more satisfactory to identify the anointing, sealing, and giving of the earnest with the single event of baptism, and the continuous establishing with the other and constantly repeated New Testament sacrament of the holy communion.[21]

Establishes us with you ... Paul affirmed in this the essential unity of all Christians, himself as well as the Corinthians, "in Christ." By virtue of unity with Christ and "in Christ," there is no fraud, insincerity or deception in any Christian, apostle or otherwise, all such evils being fundamentally opposed to their very nature in the Lord.

Sealed us ... earnest of the Spirit ... The earnest (or token) of the Holy Spirit is identified with "the Holy Spirit of promise" (Ephesians 1:13) and is the invariable inheritance of all who obey the gospel of Christ. For further discussion see my Commentary on Romans, p. 124. Even the Corinthians possessed the earnest of the Holy Spirit, despite their delinquency in so many particulars.