.... Here are some detail about the 1st and 2nd phrase. All in the form of questions. Hopefully they're "leading" questions!
BIG IDEA #1 (let's look at the 1st two phrases as a series of chords)
hypothetically, what IF the E maj triad that begins the chorale is a pickup? and the 1st chord of the 1st measure is an A min triad?
What if the last chord of the 2nd phrase (right before the double bar line) is an A minor triad?
Hypothetically, what if the 1st chord of the 2nd measure is an E maj triad (1st inversion)? And what if the 1st chord of the 3rd measure is an A min triad (first inversion)?
So just taking the 1st chord of each measure for the 1st 2 phrases (measures 1 - 4) ....
m1 -> A min
m2 -> E maj (1st inversion)
m3 -> A min (1st inversion)
m4 -> E major (C in the sop. is an upper neighbor to B, the note of resolution)
last chord of m4 -> A min
Let's put it all together (and simplify):
A min -> E maj -> A min -> E maj -> A min (What key does this look like?)
The pickup chord to m1 is an E maj triad. Let's add that to the front of the progression.
E maj -> A min -> E maj -> A min -> E maj -> A min (What key does this look and sound like?)
Let's turn those chords into Roman numerals (the V chord at the beginning is the pickup that precedes m1).
V -> i -> V - i -> V -> i
What key does this look like if the i chord is A min and V is E maj?
If we're looking only at the the chords described above we're leaving out most of the other chords in each measure (on purpose). If we didn't leave them out could we hear those chords as passing chords?
Can we take the 1st and 3rd beat of every measure. Could the chords that fall in between (chords on beat 2 and beat 4) - could they be passing chords? So, could a chord on beat 1 and a chord on beat 3 have a passing chord that falls in between on beat 2?
To put this to work in jazz (hypothetically), let's say we're playing ATTYA. 1st measure is F min7. 2nd measure is Bb min 7. Could we play an F min7 on beat 1? A C7 on beat 2? An Fm7 for beat 3 and 4? And then on to the Bb min7.
BIG IDEA #2 (let's look at the 1st 2 phrases as 4 independent lines).
Look and listen to the bass line for the 1st two phrases.
Look and listen to the tenor line for the 1st two phrases.
Look and listen to the alto line for the 1st two phrases.
Look and listen to the soprano line for the 1st two phrases.
What do you hear and see as the key for each of the lines (bass, tenor, alto, soprano).
If we were to answer all questions above would that tell us anything about the key of the first 2 phrases?
BIG IDEA #3
The very last chord of the chorale is an E maj triad. Does the chorale end on a i chord? Or a V chord?
... Hoping these questions have all been leading!