"Heaven and earth will pass away, but my words will not pass away" (Mk 13: 31). Let us pause a moment to reflect on this prophecy of Christ.
The expression "Heaven and earth" recurs frequently in the Bible in reference to the whole universe, the entire cosmos. Jesus declares that all this is destined to "pass away"; not only the earth but also Heaven, which here is meant in a purely cosmic sense and not as synonymous with God. Sacred Scripture knows no ambiguity: all Creation is marked by finitude, including the elements divinized by ancient mythologies; there is no confusion between Creation and the Creator but rather a decided difference. With this clear distinction Jesus says that his words "will not pass away", that is to say they are part of God and therefore eternal. Even if they were spoken in the concreteness of his earthly existence, they are prophetic words par excellence, as Jesus affirms elsewhere, addressing the heavenly Father: "I have given them the words which you gave me, and they have received them and know in truth that I came from you; and they have believed that you sent me" (Jn 17: 8). In a well-known parable Christ compares himself to the sower and explains that the seed is the word (cf. Mk 4: 14); those who hear it, accept it and bear fruit (cf. Mk 4: 20) take part in the Kingdom of God, that is, they live under his lordship. They remain in the world, but are no longer of the world. They bear within them a seed of eternity a principle of transformation that is already manifest now in a good life, enlivened by charity, and that in the end will produce the resurrection of the flesh. This is the power of Christ's word.
[Pope Benedict, Angelus 15 November 2009]