At the time of the complete fulfillment of this redemption, "the earnest of our inheritance" will blossom into its entire fullness. What will we be heirs of? What will we inherit?
» The Spirit itself bears witness with our spirit that we are [present tense] children of God, and if children, then heirs—heirs of God and joint heirs with Christ, if indeed we suffer with Him, that we may also be glorified together. (Romans 8:16-17)
» And if you are Christ's, then you are [present tense] Abraham's seed, and heirs according to the promise. (Galatians 3:29)
» That having been justified [past tense] by His grace, we should become heirs according to the hope of eternal life. (Titus 3:7)
» Are [angels] not all ministering spirits sent forth to minister for those who will inherit salvation? (Hebrews 1:14)
The English words "will inherit," as translated here in Hebrews 1:14 from the Greek verb méllontas, make it sound as if it is in the future tense. Grammatically, however, it is actually "active present" tense in the Greek, and therefore it might be better rendered as "those who are inheriting salvation." Nevertheless, even with human inheritances, the entirety of the inheritance does not come immediately upon an individual becoming an heir, as the actual receipt of its benefits comes later (Hebrews 9:16).
Being heirs of God and joint heirs with Christ, the total inheritance has not yet been totally given to us. So far, we have received just an earnest—a down payment—of the fullness of His Holy Spirit and the fullness of the associated blessings that we will receive in the future. Further, we have God's unbreakable promise that we will receive our full inheritance when the time comes: "Thus God, determining to show more abundantly to the heirs of promise the immutability of His counsel, confirmed it by an oath" (Hebrews 6:17).
Again, what exactly is the inheritance? What is promised to us? The apostle James makes it clear: "Listen, my beloved brethren: Has God not chosen the poor of this world to be rich in faith and heirs of the kingdom which He promised to those who love Him?" (James 2:5). As well as being an indescribable inheritance, God's Kingdom is also a firm promise to us from God. He does not break His promises!
Thy Kingdom Come! (Part One)