The thought has crossed my mind as to why New Testament believers are sealed with the Spirit when Old Testament believers were not? It seems we received a great deal. It has certainly humbled me to realize this. Can you help clarify?
Old Testament believers were not sealed with the Holy Spirit and neither are those who will come to faith after the Church is gone. Only the Church is given this blessing.
This is partly because in the Old Testament there was plenty of evidence of God’s presence, and that was the basis for their faith. He brought the rains in season, gave them victory over their enemies, and saw to it that they had a standard of living that was the envy of the known world.
This will be true during the End Times judgments as well, although in a different way. Evidence of his presence will be so obvious that even His enemies will recognize it. Rev. 16:9 says they will curse the name of God who controls the plagues they will be suffering, but they will refuse to repent and glorify Him.
But the Church was asked to believe solely by faith, and as a reward our salvation is assured. When we believed, the Holy Spirit was sealed within us as a deposit guaranteeing our inheritance, which is eternal life (John 3:16, Ephes. 1:13-14).
Paul said that through the Church, God is demonstrating the incomparable riches of His Grace, expressed in His kindness to us in Christ Jesus (Ephes. 2:6-7). Therefore, saying we received a great deal is an understatement in every sense of the word.
After Thomas demanded evidence as a condition for his belief, Jesus provided it. Then He said, “Because you have seen, you have believed. Blessed are those who have not seen and yet have believed.” (John 20:29) He was talking about us.