Objection 1. It would seem that the New Law will not last until the end of the world. Because, as the Apostle says (1 Corinthians 13:10), "when that which is perfect is come, that which is in part shall be done away." But the New Law is "in part," since the Apostle says (1 Corinthians 13:9): "We know in part and we prophesy in part." Therefore the New Law is to be done away, and will be succeeded by a more perfect state.
Objection 2. Further, Our Lord (John 16:13) promised His disciples the knowledge of all truth when the Holy Ghost, the Comforter, should come. But the Church knows not yet all truth in the state of the New Testament. Therefore we must look forward to another state, wherein all truth will be revealed by the Holy Ghost.
Objection 3. Further, just as the Father is distinct from the Son and the Son from the Father, so is the Holy Ghost distinct from the Father and the Son. But there was a state corresponding with the Person of the Father, viz. the state of the Old Law, wherein men were intent on begetting children: and likewise there is a state corresponding to the Person of the Son: viz. the state of the New Law, wherein the clergy who are intent on wisdom (which is appropriated to the Son) hold a prominent place. Therefore there will be a third state corresponding to the Holy Ghost, wherein spiritual men will hold the first place.
Objection 4. Further, Our Lord said (Matthew 24:14): "This Gospel of the kingdom shall be preached in the whole world... and then shall the consummation come." But the Gospel of Christ is already preached throughout the whole world: and yet the consummation has not yet come. Therefore the Gospel of Christ is not the Gospel of the kingdom, but another Gospel, that of the Holy Ghost, is to come yet, like unto another Law.
On the contrary, Our Lord said (Matthew 24:34): "I say to you that this generation shall not pass till all (these) things be done": which passage Chrysostom (Hom. lxxvii) explains as referring to "the generation of those that believe in Christ." Therefore the state of those who believe in Christ will last until the consummation of the world.
I answer that, The state of the world may change in two ways. In one way, according to a change of law: and thus no other state will succeed this state of the New Law. Because the state of the New Law succeeded the state of the Old Law, as a more perfect law a less perfect one. Now no state of the present life can be more perfect that the state of the New Law: since nothing can approach nearer to the last end than that which is the immediate cause of our being brought to the last end. But the New Law does this: wherefore the Apostle says (Hebrews 10:19-22): "Having therefore, brethren, a confidence in the entering into the Holies by the blood of Christ, a new... way which He hath dedicated for us... let us draw near." Therefore no state of the present life can be more perfect than that of the New Law, since the nearer a thing is to the last end the more perfect it is.
In another way the state of mankind may change according as man stands in relation to one and the same law more or less perfectly. And thus the state of the Old Law underwent frequent changes, since at times the laws were very well kept, and at other times were altogether unheeded. Thus, too, the state of the New Law is subject to change with regard to various places, times, and persons, according as the grace of the Holy Ghost dwells in man more or less perfectly. Nevertheless we are not to look forward to a state wherein man is to possess the grace of the Holy Ghost more perfectly than he has possessed it hitherto, especially the apostles who "received the firstfruits of the Spirit, i.e. sooner and more abundantly than others," as a gloss expounds on Romans 8:23.
Reply to Objection 1. As Dionysius says (Eccl. Hier. v), there is a threefold state of mankind; the first was under the Old Law; the second is that of the New Law; the third will take place not in this life, but in heaven. But as the first state is figurative and imperfect in comparison with the state of the Gospel; so is the present state figurative and imperfect in comparison with the heavenly state, with the advent of which the present state will be done away as expressed in that very passage (1 Corinthians 13:12): "We see now through a glass in a dark manner; but then face to face."
Reply to Objection 2. As Augustine says (Contra Faust. xix, 31), Montanus and Priscilla pretended that Our Lord's promise to give the Holy Ghost was fulfilled, not in the apostles, but in themselves. In like manner the Manicheans maintained that it was fulfilled in Manes whom they held to be the Paraclete. Hence none of the above received the Acts of the Apostles, where it is clearly shown that the aforesaid promise was fulfilled in the apostles: just as Our Lord promised them a second time (Acts 1:5): "You shall be baptized with the Holy Ghost, not many days hence": which we read as having been fulfilled in Acts 2. However, these foolish notions are refuted by the statement (John 7:39) that "as yet the Spirit was not given, because Jesus was not yet glorified"; from which we gather that the Holy Ghost was given as soon as Christ was glorified in His Resurrection and Ascension. Moreover, this puts out of court the senseless idea that the Holy Ghost is to be expected to come at some other time.
Now the Holy Ghost taught the apostles all truth in respect of matters necessary for salvation; those things, to wit, that we are bound to believe and to do. But He did not teach them about all future events: for this did not regard them according to Acts 1:7: "It is not for you to know the times or moments which the Father hath put in His own power."
Reply to Objection 3. The Old Law corresponded not only to the Father, but also to the Son: because Christ was foreshadowed in the Old Law. Hence Our Lord said (John 5:46): "If you did believe Moses, you would perhaps believe me also; for he wrote of Me." In like manner the New Law corresponds not only to Christ, but also to the Holy Ghost; according to Romans 8:2: "The Law of the Spirit of life in Christ Jesus," etc. Hence we are not to look forward to another law corresponding to the Holy Ghost.
Reply to Objection 4. Since Christ said at the very outset of the preaching of the Gospel: "The kingdom of heaven is at hand" (Matthew 4:17), it is most absurd to say that the Gospel of Christ is not the Gospel of the kingdom. But the preaching of the Gospel of Christ may be understood in two ways. First, as denoting the spreading abroad of the knowledge of Christ: and thus the Gospel was preached throughout the world even at the time of the apostles, as Chrysostom states (Hom. lxxv in Matth.). And in this sense the words that follow--"and then shall the consummation come," refer to the destruction of Jerusalem, of which He was speaking literally. Secondly, the preaching of the Gospel may be understood as extending throughout the world and producing its full effect, so that, to wit, the Church would be founded in every nation. And in these sense, as Augustine writes to Hesychius (Epist. cxcix), the Gospel is not preached to the whole world yet, but, when it is, the consummation of the world will come.
Source: Summa Theologica (New Advent)