The relevant section in w 07/15/13 p.16 para.8 reads :
Starting at Pentecost 33 C.E., the resurrected Christ used his apostles as the channel through which he fed the rest of his anointed disciples. (Read Acts 2:41, 42.) That channel was clearly recognized by the Jews and proselytes who became spirit-anointed Christians that day. Unhesitatingly, they “continued devoting themselves to the teaching of the apostles.” According to one scholar, the Greek verb rendered “continued devoting themselves” can mean having “a steadfast and singleminded fidelity to a certain course of action.”
The scholar referred to is Richard N. Longenecker and his discussion of Acts 2:42 in The Expositor's Bible Commentary: Acts, ed. Frank Gaebelein (Grand Rapids: Zondervan, 1981), p.289 where he wrote:
Luke begins to describe the early church by telling us that the believers in it were distinguished by their devotion to the apostles' teaching, to fellowship with one another, to "breaking of bread," and "to prayer." The verb translated "devoted" (proskartereo) is a common one that connotes a steadfast and singleminded fidelity to a certain course of action. Luke uses it elsewhere in Acts to characterize the devotion of the 120 in the upper room to prayer (1:14) and the apostles’ resolve in the matter of the Hellenistic widows to center their attention on prayer and the ministry of the word (6:4)
"The apostles’ teaching” refers to a body of material considered authoritative because it was the message about Jesus of Nazareth proclaimed by accredited apostles.