The Apostles laid the foundation. The foundation is not still being built.
Agreed.
"having been built upon
the foundation of the apostles and prophets, Christ Jesus Himself being
the cornerstone" - Eph2:20.
Paul is also an
"apostle" according to
2Cor1:1, Gal1:1, Eph1:1, Col1:1... yet he is
not "one of the 12" like
Matthias in Acts 1:20-26 came to be -
20 “For it has been written in
the book of Psalms:
‘Let his homestead become desolate,
and let there be not
one dwelling in it,’
d
and,
‘Let another
take his position.’
e
21 Therefore it behooves the men having accompanied us during all
the time that the Lord Jesus came in and went out among us,
22 having begun from the baptism of John until the day in which He was taken up from us, one of these, to become a witness with us of His resurrection.”
23 And they put forward two, Joseph called Barsabbas, who was called Justus, and
Matthias.
24 And having prayed, they said, “You Lord, knower of the hearts of all,
show which one of these two You have chosen 25 to take the place of this ministry
and apostleship, from which Judas turned aside to go to the own place.”
26 And they gave lots for them,
and the lot fell on Matthias,
and he was numbered with the eleven apostles.