What guarantees that God will redeem our bodies?
The indwelling Holy Spirit serves as God's down payment and seal on our bodies, guaranteeing future redemption. Though the soul and spirit are redeemed at salvation, the body awaits a new body reunited with soul and spirit for eternity. The Holy Spirit's presence assures this regardless of death or disaster.
Les teaches that the adoption is the redemption of our body. At salvation, the soul and spirit are totally redeemed, saved, and made ready for eternity, but the old body is not ready yet. God has put His down payment on it by virtue of the indwelling Holy Spirit, which is His brand on us. That guarantees that regardless of whether we go through the valley of the shadow of death and are put in the cemetery, or some other bizarre disaster happens, one day we will have a new body reunited with the soul and spirit, so that we are a complete entity for the eternal. Les also connects this to II Corinthians 5, where while we are at home in the body we are absent bodily from the Lord, though spiritually we are already citizens of heaven, translated into the kingdom of His dear Son.
Now he that hath wrought us for the selfsame thing is God, who also hath given unto us the earnest of the Spirit.