Visuddhimagga IV-144

Nanu cāyaṃ saddhā paṭhamajjhānepi atthi, ayañca ekodināmako samādhi, atha kasmā idameva ‘‘sampasādanaṃ cetaso ekodibhāvañcā’’ti vuttanti.

在初禅岂不是也有此「信」和「专一」而名为定，为什么仅（在第二禅）而称为「净心专一」呢？

Ñ(IV,144): It might be asked: But does not this faith exist in the first jhāna too, and also this concentration with the name of the 'single [thing]'? Then why is only this second jhāna said to have confidence and singleness of mind? —

Vuccate, aduñhi paṭhamajjhānaṃ vitakkavicārakkhobhena vīcitaraṅgasamākulamiva jalaṃ na suppasannaṃ hoti, tasmā satiyāpi saddhāya ‘‘sampasādana’’nti na vuttaṃ.

答道：[PTS 157] 因为初禅为寻伺所扰乱，犹如给波浪所动乱的水，不是很净的，所以初禅虽也有信，但不名为「净」。

Ñ: It may be replied as follows: It is because that first jhāna [157] is not fully confident owing to the disturbance created by applied and sustained thought, like water ruffled by ripples and wavelets. That is why, although faith does exist in it, it is not called 'confidence'.

Na suppasannattāyeva cettha samādhipi na suṭṭhu pākaṭo, tasmā ‘‘ekodibhāva’’ntipi na vuttaṃ.

因不很净，则三摩地亦不甚明了，所以亦不名为专一。

Ñ: And there too concentration is not fully evident because of the lack of full confidence. That is why it is not called 'singleness' there.

Imasmiṃ pana jhāne vitakkavicārapalibodhābhāvena laddhokāsā balavatī saddhā, balavasaddhāsahāyapaṭilābheneva ca samādhipi pākaṭo, tasmā idameva evaṃ vuttanti veditabbaṃ.

在二禅中已无寻伺的障碍而得强信生起的机会。得与强信作伴，则三摩地亦得明了，故知仅于二禅作这样说。

Ñ: But in this second jhāna faith is strong, having got a footing in the absence of the impediments of applied and sustained thought; and concentration is also evident through having strong faith as its companion. That may be understood as the reason why only this jhāna is described in this way.