Question: It is commonly taught that Purelanders will only take one more rebirth before becoming a Buddha. However, it is also said that prior to attaining Buddhahood in the human realm, Buddhas-to-be will have to be reborn in Tusita heaven first. Is there a contradiction?
Answer: If we look at Vow #22 of Amituofo (paying attention to the part in bold), we will realise that not all Purelanders are only one life away from Buddhahood – if they can choose to manifest many more lives as practising Bodhisattvas to help others first. But many other Purelanders do indeed choose to reach the Stage Of One Life To Replacement (of other Buddhas) in Pure Land.
 Vow Of Bodhisattvas Attaining Stage Of One Life To Replacement [Of Other Buddhas; Eka-jati-prati-baddhas]
If I [Dharmakara Bodhisattva, who had 10 kalpas (world cycles) ago become Amitabha Buddha] attain Buddhahood, all other directions’ Buddha Lands’ Bodhisattva assemblies, who come to be born in my land will ultimately and definitely attain the Stage Of One Life To Replacement [of other Buddhas]. Excluded are those whose fundamental vows are to, with ease manifest, for sentient beings thus, wear the great armour of vows [spiritual aspirations], accumulate the roots of virtues, and liberate all [beings]. Travelling to all Buddha Lands [defiled and pure], cultivating Bodhisattva practices, making offerings to all the ten directions’ Buddha Tathagatas, guide and transform immeasurable sentient beings, [as numerous as the] Ganges [River’s] sands, causing them to be established on the unsurpassable, right and true path [to Buddhahood]. Exceeding ordinary peers of all grounds in practice, [they will] directly manifest cultivation of the virtues of Samantabhadra [Bodhisattva]. If not so, [I shall] not attain right awakening.
When Purelanders reach the Stage Of One Life To Replacement, their subsequent manifestations into Tusita is just part of fulfilling the standard process of the ‘Eight Forms On Accomplishment Of Buddhahood’. These are skilful manifestations done out of compassion to exemplify the path to Buddhahood (as ‘teaching aids’), when there is no real ‘karmic requirement’ to do so on their part. For example, the diligently surveying of the human world from Tusita by Buddhas-to-be to choose the conditions of birth to best benefit the most beings are demonstrations of their great deliberated compassion. Thus, technically, that birth in Tusita cannot be counted as one more mundane birth into Samsara, especially since there will be absolutely no samsaric suffering in Tusita for Buddhas-to-be. In this way, this particular birth presents no problems in any sense to anyone.