The first is sila visuddhi, Purification of Moral Conduct. Meditators have to observe at least five precepts, if not eight, so that they can attain purification of sila. The third of the five precepts is abstention from sexual misconduct, whereas the third of the eight precepts is abstention from all kinds of sexual contact. If a meditator does not abstain from sexual contact, his mind will be defiled by the hindrance of sense desire kamacchanda nivarana). Only when the mind is purified from all hindrances can meditators realise mental and physical processes in their true nature.
Of course it is better if meditators can observe the eight precepts. If they do not, they may have desires for taste, food, visible things, audible things, odours and tangible things - five kinds of sense desire (kammacchanda) in their mind. By observing eight precepts, one can purify ones deeds and speech which is purification of moral conduct (Citta visuddhi). When moral conduct is purified, the mind is also purified to some extent.
When the mind becomes purified, it becomes calm, serene, tranquil and happy and can concentrate on the object of meditation. Then the meditator attains Purification of Mind, i.e. Citta visuddhi the second stage of purification.
When Venerable Uttiya, one of the disciples of the Buddha was sick in bed, the Buddha visited him and asked about his health. Venerable Uttiya told the Buddha about his sickness:
Venerable sir, my sickness is not decreasing but increasing. I do not know whether I can or cannot live out today or tomorrow. So I want to meditate to destroy all kinds of defilements through to the fourth stage of enlightenment, arahantship, before I die. Please give a short instruction which will enable me to develop my meditation practice to attain Arahantship.
Then the Buddha said:
Uttiya, you should cleanse the beginning. If the beginning is purified, then you will be all right, i.e. able to attain Arahantship.
The Omniscient Buddha asked the question, "What is the beginning?" He himself replied, "Herein the beginning is purified moral conduct or sTia and right view (Samma ditthi). Right view means the acceptance of and belief in the Law of Cause and Effect (action reaction) or the Law of Kamma." The Omniscient Buddha continued:
Uttiya, you should cleanse your moral conduct and right view. Then, based on the purified moral conduct or Sila, you should develop the Four Foundations of Mindfulness. Practising thus, you will attain the cessation of suffering.
The Omniscient Buddha lays stress on the purification of sila or moral conduct because it is a basic requirement for progress in concentration as well as insight. When moral conduct is purified, the mind becomes calm, serene and happy. If he cultivates mindfulness, then he can easily concentrate on any object of the mental and physical processes. So purity of moral conduct is a pre requirement for a meditator to make progress.