Whoops, I goofed. As noted by many in the comments, I picked up the sermon from a later Samuel Seabury. (Hang around for awhile and I'll tell you about Martin Luther's famous "I have a dream" speech.)
I wonder how he would fare today?
Look at this sermon in which he examines a particular doctrine espoused by the Anglican Church, that our Lord's human nature "was, from the first moment of its existence, void of all spot or taint of sin."
Let us walk with Bishop Seabury to see how Doctrine is derived.
First, he tells us we believe this doctrine "because it has been delivered to us by the Church as a necessary article of the Christian faith." It traces back to "[t]he apostles, themselves, or at least their successors at a very early age of the Church..." and is " necessary to guard the original faith from the assaults and wiles of those who sought to deprave it by false and heretical teaching."
Is tradition alone, Rev. Seabury, sufficient grounding for Doctrine?
this prescription, which may plead apostolic tradition in its favor; this teaching of our common mother, which ought in reason to have far more weight with us than the wisest of human parents, is a sufficient ground for our belief in the doctrine, at least in the first instance, and until we shall be qualified to try our faith by the ultimate standard of Holy Scripture.(emphasis added).
How should we proceed?
...you proceed, as in an humble and reverential spirit you properly may, to compare the teaching of the Church with the infallible dictates of Holy Scripture...
Bishop Seabury continues: "Human testimony is the ground of human faith, or that which we exercise in the common affairs of life. Divine testimony is the ground of divine faith, or that which is required of us in order to our everlasting salvation."
In the second portion of his sermon, he turns from the grounds of Doctrine to "the use of" or reason for the Doctrine. As Seabury puts it: "For God does nothing for naught, and weak as we are we can always discover enough in His works to excite our admiration of His wisdom and goodness."
The rest of the sermon is excellent and I commend it to you -- it is, essentially a refutation of what was then a recent development in the Church of Rome, the Doctrine of the Immaculate Conception of Mary. The importance for us is that he develops Doctrine based on the Apostolic teachings handed down, subject always to the ultimate standard, the Word of God.
What a fundamentalist!
More. From this it looks like Seabury only bases Doctrine on two of the three legs of the Anglican stool. What about the third leg, reason?
In this sermon he does reaffirm the three legs, but again note that it must comport with "plain Scripture:
...truth which is conveyed to faith in regard to the invisible and spiritual must correspond to all that is expressed to the senses in regard to the visible and material, provided that nothing be received which is contradictory to reason and plain Scripture.