Commentary Mahaaraahulovadasutta, 14 B.
Relevant Sutta passage:
Addasaa kho aayasmaa saariputto aayasmanta.m Raahula.m a~n~natarasmi.m
rukkhamuule nisinna.m palla'nka.m aabhujitvaa uju.m kaaya.m
pa.nidhaaya parimukha.m sati.m upa.t.thapetvaa. Disvaana aayasmanta.m
Raahula.m aamantesi : aanaapaanasati.m Raahula bhaavana.m bhaavehi,
aanaapaanasati Raahula bhaavitaa bahuliikataa mahapphalaa hoti
mahaanisa.msaa ti.

The venerable Sariputta saw the venerable Rahula seated at the foot of that
tree, cross-legged and body upright with mindfulness established before him.
Having seen the venerable Rahula, he addressed him: "Cultivate the
development of mindfulness on in and out breathing, Rahula. The
development of mindfulness on in and out breathing, Rahula, is of
great fruit and profit."

Commentary:
Words:
niyojeti: urge
anucchavika: suitable
aavajjeti: to consider, observe.
acala: not moving, unshakable.
baddha: bound, connected with(anobaddha : not in the dictionary).
pariga.nhaati: explore, examine, comprehend
ga.nhaati: seize, acquire.
anuyutta : engaged in (anyu~njati)
ekaasana: sitting alone
samasiisi : One who attains two ends simultaneously.
khepeti: destroy, bring to waste.
nibbatteti: to produce
viraddha: failed, missed (virajjhati)
sammuukho: face to face with
sammuukhiibhaava: being in the presence of
khippa: quick, very soon.

Commentary text 14 B:

atha kasmaa aanaapaanassatiya.m niyojesi? nisajjaanucchavikattaa.
Then, why did he exhort him to develop Mindfulness of Breathing? Because it
is suitable for a sitting posture.

thero kira ``etassa bhagavataa ruupakamma.t.thaana.m kathita''nti
anaavajjitvaava
It is said that the Thera had not observed that the Buddha had spoken about
the meditation subject of materiality to Rahula.

yenaakaarena aya.m acalo anobaddho hutvaa nisinno,
He thought that for Rahula who was seated in that way, steadfast and
immovable,

idamassa etissaa nisajjaaya kamma.t.thaana.m anucchavikanti cintetvaa
evamaaha.
that subject of meditation in such sitting posture was suitable for him, and
thus he spoke to him in that way.

tattha aanaapaanassatinti assaasapassaase pariggahetvaa tattha
catukkapa~ncakajjhaana.m nibbattetvaa
As regards the word, aanaapaanasati, mindfulness of breathing, he explained:
"After you have comprehended inbreathing and outbreathing, and with this
subject attained the fourth or the fifth stage of jhana,

vipassana.m va.d.dhetvaa arahatta.m ga.nhaahiiti dasseti.
and you have developed insight, you should reach arahatship."

mahapphalaa hotiiti kiivamahapphalaa hoti?
As to the words, it is of great fruit, how is it of great fruit?

idha bhikkhu aanaapaanassati.m anuyutto
Here, the monk who is intent on mindfulness of breathing,

sabbaasave khepetvaa arahatta.m paapu.naati.
eradicates all defilements and reaches arahatship.

tathaa asakkonto mara.nakaale samasiisii hoti,
If he cannot do this , there will be at the end of life the extinction of
all defilements **.

tathaa asakkonto devaloke nibbattitvaa
If he cannot do this, he will be reborn in a deva plane,

dhammakathikadevaputtassa dhamma.m sutvaa arahatta.m paapu.naati,
and when he has heard Dhamma from a deity (son of a deva) who is a speaker
of Dhamma, he will attain arahatship.

tato viraddho anuppanne buddhuppaade paccekabodhi.m sacchikaroti,
If this fails because the appearance of a Buddha has not taken place, he
will realize the awakening of a solitary Buddha.

ta.m asacchikaronto buddhaana.m sammukhiibhaave baahiyattheraadayo viya
khippaabhi~n~no hoti,
If he cannot realize this, he can, being in the presence of Buddhas, attain
higher knowledge *** quickly, such as the Elder Baahiya and others.

eva.m mahapphalaa.
Thus it is of great fruit.

mahaanisa.msaati tasseva vevacana.m.
As to the expression ³mahaanisa.msaa², of great benefit, this is a synonym
of ³mahapphalaa², of great fruit².

*****
English:
Then, why did he exhort him to develop Mindfulness of Breathing? Because it
is suitable for a sitting posture.
It is said that the Thera had not observed that the Buddha had spoken about
the meditation subject of materiality to Rahula.
He thought that for Rahula who was seated in that way, steadfast and
immovable, that subject of meditation in such sitting posture was suitable
for him, and thus he spoke to him in that way.
As regards the word, aanaapaanasati, mindfulness of breathing, he explained:
"After you have comprehended inbreathing and outbreathing, and with this
subject attained the fourth or the fifth stage of jhana, and you have
developed insight, you should reach arahatship."
As to the words, it is of great fruit, how is it of great fruit?
Here, the monk who is intent on mindfulness of breathing, eradicates all
defilements and reaches arahatship.
If he cannot do this , there will be at the end of life the extinction of
all defilements **.
If he cannot do this, he will be reborn in a deva plane, and when he has
heard Dhamma from a deity (son of a deva) who is a speaker of Dhamma, he
will attain arahatship.
If this fails because the appearance of a Buddha has not taken place, he
will realize the awakening of a solitary Buddha.
If he cannot realize this, he can, being in the presence of Buddhas, attain
higher knowledge *** quickly, such as the Elder Baahiya and others.
Thus it is of great fruit.
As to the expression ³mahaanisa.msaa², of great benefit, this is a synonym
of ³mahapphalaa², of great fruit².

______
* There are more versions: the Burmese edition has: acalo anabandho.
The PTS edition has: acalaasanabandho hutvaa, motionless, glued to his seat.
** samasiisi, who attains two ends simultaneously, who at the end of his
life eradicates all defilements.
*** The subcommentary glosses: ³the six higher knowledges². These include
higher spiritual powers. The sixth one is the eradication of all
defilements.

********
Nina.