The Contemplation

"This is eternal life: that they may know you, the only true God" John 17:3.  To know God is contemplation, explains Tomas Aquinas.
Aristotle also explains that contemplation or contemplative activity is a perfect activity. An activity related with the wisdom, with the wise, as a result is asociated with a form of happinees, different that the happiness related with virtue. Tomas Aquinas continues this reasoning and affirm: "Eternal happiness consist in the vision of God", Summa Theologiae.
There is a beatitude related with eternal life: "Blessed are the pure in heart for they shall see God" Matthew 5:8. The purity of heart (lack of selfishness) is a requirement for eternal life.
Tomas Aquinas also explains that angels are created for the contemplation of God, for the vision of God. The contemplation is the main activity of the angel, his purpose.
http://www.quintoevangelio.com.ar/en/articles/item/40-eternal-life.html