This question is well answered by MN 27 and the commentary of its translator, Ven. Thanissaro.
According to the sutta, the one who attains the four jhanas, the knowledge of past lives/ abodes recollection and the knowledge of beings passing away and reappearing, is not yet able to come to the conclusion (i.e. have unshakable faith, or have no doubt at all) regarding the Buddha, the Dhamma and the Sangha:
"This, too, is called a footprint of the Tathagata, a scratch mark of
the Tathagata, a tusk slash of the Tathagata, but a disciple of the
noble ones would not yet come to the conclusion, 'The Blessed One is
rightly self-awakened; the Dhamma is well-taught by the Blessed One;
the Sangha of the Blessed One's disciples has practiced rightly.'
However, the sutta continues:
"With his mind thus concentrated, purified, and bright, unblemished,
free from defects, pliant, malleable, steady, and attained to
imperturbability, the monk directs and inclines it to the knowledge of
the ending of the mental fermentations. He discerns, as it has come to
be, that 'This is stress... This is the origination of stress... This
is the cessation of stress... This is the way leading to the cessation
of stress... These are mental fermentations... This is the origination
of fermentations... This is the cessation of fermentations... This is
the way leading to the cessation of fermentations.'
"This, too, is called a footprint of the Tathagata, a scratch mark of
the Tathagata, a tusk slash of the Tathagata. A disciple of the noble
ones has not yet come to conclusion, but he comes to the conclusion,
'The Blessed One is rightly self-awakened; the Dhamma is well-taught
by the Blessed One; the Sangha of the Blessed One's disciples has
practiced rightly.'
So, when he fully understands the four noble truths, only then does he come to the conclusion (i.e. have unshakable faith, or have no doubt at all) regarding the Buddha, the Dhamma and the Sangha. But he himself has not yet come to a conclusion, i.e. he is not yet an Arahant.
So, what is his attainment at this stage?
Ven. Thanissaro, the translator, comments:
This stage in the practice would seem to correspond to reaching
stream-entry, inasmuch as one of the standard definitions of
stream-entry is direct vision of the four noble truths. It is also the
stage at which one reaches unwavering conviction in the Buddha,
Dhamma, and Sangha.
The sentence stating that the stream-enterer has come to a conclusion
without coming to conclusion is a play on words. The idiomatic
expression for coming to a conclusion — ni.t.tha.m gacchati — can also
mean coming to a finish, reaching completion, or coming to an end. To
distinguish these two meanings, the text here uses the form
ni.t.tha.ngato to mean having come to a finish, and ni.t.tha.m
gacchati to mean coming to a conclusion.
That means only the one who has gained stream entry could have unshakable faith in the Buddha, the Dhamma and the Sangha.
Then the sutta goes on to describe the Arahant (who comes to a conclusion):
"His heart, thus knowing, thus seeing, is released from the
fermentation of sensuality, the fermentation of becoming, the
fermentation of ignorance. With release, there is the knowledge,
'Released.' He discerns that 'Birth is ended, the holy life fulfilled,
the task done. There is nothing further for this world.'
"This, too, is called a footprint of the Tathagata, a scratch mark of
the Tathagata, a tusk slash of the Tathagata, and it is here that a
disciple of the noble ones has come to conclusion: 'The Blessed One is
rightly self-awakened; the Dhamma is well-taught by the Blessed One;
the Sangha of the Blessed One's disciples has practiced rightly.'"