What is the indwelling Holy Spirit as a result of our salvation?
The indwelling Holy Spirit is the seal and earnest of salvation: after believing the Gospel, the believer is sealed with the Holy Spirit of promise, who is the down payment of the inheritance, guaranteeing it until the redemption of the purchased possession, when the body is redeemed.
Les explains from Ephesians 1:13-14 that after a person hears the word of truth, the Gospel of salvation, and believes, that person is sealed with the Holy Spirit of promise. This sealing is part and parcel of the salvation experience: the believer has been marked by the person of the Holy Spirit Himself. Verse 14 calls Him the earnest, meaning the down payment, a sufficient down payment to make sure the transaction is completed. So the indwelling Holy Spirit as a result of salvation is the down payment of our inheritance, which we will have by being joint heirs with Christ, and He holds it until the redemption of the purchased possession under the praise of His glory. Les also connects this to 1 Corinthians 15, noting that soul and spirit are redeemed in full—we are saved and redeemed completely for all eternity—but the body is left and awaits redemption.
Which is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of his glory.