Aristotle believed virtues led to happiness
The happiness that Aristotle spoke of was not necessarily the same that we would think of today. Today our view of happiness tends to be hedonic. We want to feel good immediately and tend not to think too far ahead. So we see a night out or a pleasant activity as a route to happiness.
The ancient Greeks had a very different perspective on happiness. Aristotle spoke about achieving eudaimonia, which is roughly translated into happiness.
Eudaimonia is not an emotional state; it is more about being all that you can, fulfilling your potential. The idea is that by living in a way that reaches your full potential you bloom or flourish and so display the best version of you that you can be.
Aristotle thought that the practice of virtues would equate to happiness, in the sense of being all you could be. By virtues, Aristotle meant the act of achieving balance and moderation.
For example, courage would be the balance and moderation between excessive amounts, rashness and insufficient amounts, cowardice. Generosity would be the mid-ground between being a wasteful spendthrift and being a miser.
He strongly disagreed with Socrates who knowledge would automatically lead to the right action. Aristotle argued that the greatest misdeed was to know the right course, but fail to do it.
So for him it was the act of living in balance and moderation that brought the highest pleasure. Not in the action itself, but in the way of life. It is this way of life that would lead to the greatest long-term value rather than just a passing amusement. A modern illustration would be the difference between earning a high income, but spending it all and living in more moderation and having great wealth that will last you and provide security.
It was Aristotle’s belief that by achieving these virtues, happiness would result. So for him contemplation was the highest activity humans could do. Contemplation is the activity that refines and discovers virtues. Carried out continuously it allows you to reach your potential.