Objection 1. It would seem that eternal happiness is not the proper object of hope. For a man does not hope for that which surpasses every movement of the soul, since hope itself is a movement of the soul. Now eternal happiness surpasses every movement of the human soul, for the Apostle says (1 Corinthians 2:9) that it hath not "entered into the heart of man." Therefore happiness is not the proper object of hope.
Objection 2. Further, prayer is an expression of hope, for it is written (Psalm 36:5): "Commit thy way to the Lord, and trust in Him, and He will do it." Now it is lawful for man to pray God not only for eternal happiness, but also for the goods, both temporal and spiritual, of the present life, and, as evidenced by the Lord's Prayer, to be delivered from evils which will no longer be in eternal happiness. Therefore eternal happiness is not the proper object of hope.
Objection 3. Further, the object of hope is something difficult. Now many things besides eternal happiness are difficult to man. Therefore eternal happiness is not the proper object of hope.
On the contrary, The Apostle says (Hebrews 6:19) that we have hope "which entereth in," i.e. maketh us to enter... "within the veil," i.e. into the happiness of heaven, according to the interpretation of a gloss on these words. Therefore the object of hope is eternal happiness.
I answer that, As stated above (Article 1), the hope of which we speak now, attains God by leaning on His help in order to obtain the hoped for good. Now an effect must be proportionate to its cause. Wherefore the good which we ought to hope for from God properly and chiefly is the infinite good, which is proportionate to the power of our divine helper, since it belongs to an infinite power to lead anyone to an infinite good. Such a good is eternal life, which consists in the enjoyment of God Himself. For we should hope from Him for nothing less than Himself, since His goodness, whereby He imparts good things to His creature, is no less than His Essence. Therefore the proper and principal object of hope is eternal happiness.
Reply to Objection 1. Eternal happiness does not enter into the heart of man perfectly, i.e. so that it be possible for a wayfarer to know its nature and quality; yet, under the general notion of the perfect good, it is possible for it to be apprehended by a man, and it is in this way that the movement of hope towards it arises. Hence the Apostle says pointedly (Hebrews 6:19) that hope "enters in, even within the veil," because that which we hope for is as yet veiled, so to speak.
Reply to Objection 2. We ought not to pray God for any other goods, except in reference to eternal happiness. Hence hope regards eternal happiness chiefly, and other things, for which we pray God, it regards secondarily and as referred to eternal happiness: just as faith regards God principally, and, secondarily, those things which are referred to God, as stated above (Question 1, Article 1).
Reply to Objection 3. To him that longs for something great, all lesser things seem small; wherefore to him that hopes for eternal happiness, nothing else appears arduous, as compared with that hope; although, as compared with the capability of the man who hopes, other things besides may be arduous to him, so that he may have hope for such things in reference to its principal object.
Source: Summa Theologica (New Advent)