Scientists and philosophers have been able to learn many wonderful things about the universe when they have attempted reverently to think God's thoughts after Him, but His majesty and purposes are still far beyond human words and understanding--unspeakable and unsearchable. He "doeth great things and unsearchable; marvelous things without number" (Job 5:9).
Not only are His judgments unsearchable and His ways past finding out, but so are His resources. The apostle Paul spoke about "the unsearchable riches of Christ" (Ephesians 3:8), and he once had the unique experience of being caught up somehow into the very paradise of God, where he "heard unspeakable words, which it is not lawful for a man to utter" (2 Corinthians 12:4).
We shall learn more, in the ages to come, of "the exceeding riches of his grace" (Ephesians 2:7), as well as the depth of "the love of Christ, which passeth knowledge" (3:19).
We can have a good measure of peace and joy right now in Christ, but there is much more yet to learn. In the new Earth some day we shall really experience "the peace of God, which passeth all understanding" (Philippians 4:7), and be able to "rejoice with joy unspeakable and full of glory" (1 Peter 1:8).
His great gift of salvation and eternal life we comprehend only faintly now, but we know it is indeed a gift of love and grace and peace and joy! Although we cannot begin to describe it now, we can simply say in gratitude, "Thanks be unto God for his unspeakable gift" (2 Corinthians 9:15). HMM