"The martyr Tyndale, referring to the state of the dead, declared: “I confess openly, that I am not persuaded that they be already in the full glory that Christ is in, or the elect angels of God are in. Neither is it any article of my faith; for if it were so, I see not but then the preaching of the resurrection of the flesh were a thing in vain.” —William Tyndale, Preface to New Testament (ed. 1534). Reprinted in British Reformers—Tindal, Frith, Barnes, page 349. GC 547.1"
"And if Christ be not risen, then is our preaching vain, and your faith is also vain."
Both passages touch on the importance of the resurrection. Tyndale, as quoted by EGW, suggests that preaching the resurrection would be in vain if the dead were already in full glory. Paul, in 1 Corinthians 15:14, states that if Christ is not risen, then preaching is vain. The connection is that both link the validity of preaching/faith to the resurrection, although in slightly different contexts.
"It is an undeniable fact that the hope of immortal blessedness at death has led to a widespread neglect of the Bible doctrine of the resurrection. This tendency was remarked by Dr. Adam Clarke, who said: “The doctrine of the resurrection appears to have been thought of much more consequence among the primitive Christians than it is now! How is this? The apostles were continually insisting on it, and exciting the followers of God to diligence, obedience, and cheerfulness through it. And their successors in the present day seldom mention it! So apostles preached, and so primitive Christians believed; so we preach, and so our hearers believe. There is not a doctrine in the gospel on which more stress is laid; and there is not a doctrine in the present system of preaching which is treated with more neglect!”— Commentary, remarks on 1 Corinthians 15 , paragraph 3. GC 547.2"
"Now if Christ be preached that he rose from the dead, how say some among you that there is no resurrection of the dead?"
EGW is directly quoting and commenting on 1 Corinthians 15, making it an explicit allusion rather than just a direct principle.
"That is what we are to wait and watch for. The dead are already passed into glory. They do not wait for the trump for their judgment and blessedness.” GC 547.3"
"For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first:"
Both passages discuss the resurrection of the dead at the sound of a trumpet. EGW's statement contradicts the plain reading of 1 Thessalonians 4:16, but it is still thematically related.