After studying AN 5.159 Udayi Sutta and MN 24. Ratha-vinita Sutta (Relay Chariots), I'd like to add that to my understanding only a stream winner (the 2nd of the 8 types of noble disciples) who has gained the path knowledge (step 6 in MN 24) and possess the other four qualities can teach the Dhamma to others. Of course those who haven't possessed these five qualities can always point others to the Dhamma and Vinaya. :anjali:
AN 5.159: Udayi Sutta [http://www.accesstoinsight.org/tipitaka/an/an05/an05.159.than.html]
"It's not easy to teach the Dhamma to others, Ananda. The Dhamma should be taught to others only when five qualities are established within the person teaching. Which five?
" The Dhamma should be taught with the thought, 'I will speak step-by-step.' [For the Buddha's typical step-by-step teaching see Ud 5.3: Kuṭṭhi Sutta; to my understanding the step-by-step talk is more concerning the theoretical understanding, instead of the actual practice]
" The Dhamma should be taught with the thought, 'I will speak explaining the sequence [of the path/practice] (I changed the sequence "of the course and effect" into the sequence "of the path/practice", since the sequence of course and effect is included in the step-by-step theoretical talk; if the Buddha meant explaining course and effect, then he would more likely directly say "course and effect", instead of just saying "the sequence").'
" The Dhamma should be taught with the thought, 'I will speak out of compassion.'
" The Dhamma should be taught with the thought, 'I will speak not for the purpose of material reward.'
" The Dhamma should be taught with the thought, 'I will speak without hurting myself or others.'
MN 24. Ratha-vinita Sutta: Relay Chariots
[The following translation and "commentary" are based upon my personal understanding:]
“… In the same manner (as the relay of chariots),
 sīlavisuddhi (precepts/morality purity) is for cittavisuddhatthā (mind purification [samadhi]),
 citta-visuddhi (mind purity) is for diṭṭhi-visuddhatthā (view purification [Understanding the three characteristics (anicca/dukkha/anatta) and breaking of the fetter of self view]),
 diṭṭhi-visuddhi (view purity) is for kaṅkhāvitaraṇa-visuddhatthā (doubt-overcoming purification [breaking the fetter of doubt about the Buddha and the Dhamma]),
 kaṅkhāvitaraṇa-visuddhi (purity from doubt) is for maggāmaggañāṇadassana visuddhatthā (purification of path/non-path knowledge [gaining the noble right view of the 4NT in one of the three ways and four of the twelve folds, breaking the fetter of grasping sila and rituals]),
 and maggāmaggañāṇadassanavisuddhi (purity of path/non-path knowledge) is for paṭipadāñāṇadassana-visuddhatthā (purification of knowledge of the [NOBLE 8-fold] path),
 paṭipadāñāṇadassana-visuddhi (purity of knowledge of the path) is for ñāṇadassana-visuddhatthā (purification of [liberating] knowledge and insight [comprehension of the four noble truths in three ways and twelve folds & cessation of ignorance]),
 ñāṇadassana-visuddhi (purity of knowledge and insight) is for final Nibbana without grasping.
It is for Nibbana without grasping that the holy life is lived in the dispensation of the Blessed One.”