Blessed are the pure in heart, for they shall see God. Matthew 5:8

The Beatitudes in the Gospel of Matthew are 8 and in the Gospel of Luke 4. The Beatitudes refers to the spiritual gifts as explained by Thomas Aquinas in his book Summa Theologica, and are the starting point of the doctrine of the kingdom of God, the Beatitudes  are perfections and excellences and always begin with the word "happy".
The concept of happiness is central in the Gospels but not the opinated happiness or the false happiness of the Gospel of Luke with the 4 misfortunes(Luke 6:24-26). The beatitudes are about the search for true happiness and the true good of man.
There are different ways to be happy, even there are ways of happiness that arises of others unhappiness. Happiness is not all good. Remember that the opposite of happiness is the suffering.
Basically there are three forms of happiness. The first happiness is that which arises from pleasure, this would be a form of hedonic happiness. Such happiness is a momentary happiness, for moments we are happy or not.
A second type of happiness is that which is born from the effort and the hard work, this kind of happiness is more durable than previous and is related with the minimization of suffering. We work to minimize the error and the suffering and as a result we are happy. This is the happiness of the blessed.
Finally we have the happiness of the heart that comes from the contemplative activity,"see God" or "know God" in the Gospels means to Contemplate God and this is eternal life, remember the teaching: "this is eternal life: that they may know you, the only true God. John 17:3.  This is the happiness that refers the beatitude of Mark, the contemplation is the angelic activity properly, the angels are created by God for the contemplación, teach Thomas Aquinas. This kind of happiness, the happiness wich is born of the good feelings and a pure heart, is the good happiness.
The happiness of the heart is the happiness of those who listen, it is the happiness of the life in God´s grace. Is the happiness that arises from the eternal life or Contemplative activity (see article about eternal life), the good happiness. Is the happiness asociated to the spiritual love or Agape also known as love for the good.