Good Indeed, Good Indeed, Awakening to the "Who"
In the course of meditation, one may attain to the First, Second, Third, and Fourth Dhyanas. Prior to attaining the First Dhyana, one first attains a state of lightness and ease, which is quite comfortable and enjoyable. When you attain this state of being filled with Dharma bliss, you can go without food and not feel hungry, go without sleep and not feel tired, and even go naked and not feel cold. This is a state attained in the initial stages of cultivation. Whether you are sitting or walking, you feel as if you have no self. You don't know where your ego went.
Cultivation is a matter of the mind, not the legs. If you can be free of discursive thoughts, then you can practice in any posture at all. If your mind is filled with discursive thoughts, then you won't succeed in your practice no matter how you sit.
After the state of lightness and ease, you enter the samadhi of the First Dhyana. At that time, the self is empty and your pulse appears to stop. You pervade empty space and the Dharma Realm, and one or two hours of sitting seem to go by in only a second's time. However, you should not think of yourself as extraordinary; you have only gotten a tiny taste of samadhi in this initial stage of practice. Your pulse has stopped, and the next step is that your breath stops. When external breathing ceases and you no longer breathe through your nose, an internal "true" breathing begins to function. At that point, you no longer need to rely on external breathing. As you continue to progress in your practice, your thoughts will cease. When not a single thought arises and all discursive thoughts are gone--emptied--you become one with Nature. Although thoughts are said to cease in this third stage, you actually still have a thought of coarse ignorance.
In the fourth stage, thoughts are truly ended; all thoughts are renounced. This state of meditation is the Fourth Dhyana, which is still subject to outflows. You have neither ended birth and death nor realized any fruition (of sagehood). To reach the level of a First Stage Arhat, one has to cut off eighty-one grades of view delusions. View delusions occur when one gives rise to greed and desire when confronted by states. One is confused by what one sees. First Stage Arhats are called Stream-Enterers, for they enter the flow of the Dharma nature of Sages and go against the stream of the six sense objects of ordinary beings. Sages of the first fruition do not enter into forms, sounds, smells, tastes, objects of touch, or dharmas. Forms cannot move them; sounds cannot move them; smells cannot move them; flavors cannot move them; touches cannot move them; and mental dharmas cannot move them. They are not affected by the states of the six defiling objects. That's at the level of the First Stage of Arhatship. Right now, we have not even reached the First Dhyana in our meditation. None of us have felt our pulses stop beating.
If you haven't attained these states, you should work hard in every minute and second; it's important not to waste time. It's best to sit in full lotus. If you cannot, then you can sit in half lotus. If full lotus and half lotus are both too difficult, then simply sit casually. Cultivation is a matter of the mind, not the legs. If you can be free of discursive thoughts, then you can practice in any posture at all. If your mind is filled with discursive thoughts, then you won't succeed in your practice no matter how you sit. Practice consists of cultivating the mind and nurturing the nature. You must constantly observe your discursive thoughts to see what kind of thoughts are predominant. Are the majority of your thoughts concerning greed and desire? Do your thoughts contain more anger and rage than anything else? Does stupidity dominate your thinking? Reflect inwardly and examine yourself. If you can purify your mind of these discursive thoughts, you are having a response in your work. Whether you sit in full lotus, in half lotus, or casually, the essential thing is to get rid of discursive thoughts so that genuine wisdom can appear. As long as the false is not ended, the true will not manifest. In cultivating we work on the mind-ground. That is called the Mind Ground Dharma door: causing the mind to become pure. If you can be pure for one instant, you are on Magic Mountain in that one instant. If you can be pure at all times, you are always on Magic Mountain. Regardless of whether you recite the Buddha's name, hold mantras, keep the precepts, expound the teachings, or sit in Chan meditation, the goal is to focus the mind on a single point, to cast out the false and retain the true. At all times, look within yourself and recognize your original face.
That is the method to use at the initial stages of practice.
p.202 - 203, "In Memory of the Ven. Master Hsuan Hua, Vol. III"