Question: "I am not opposed to triune immersion, but I do want to question the idea that triune immersion is the ONLY way. Why isn't there a single mention of triune immersion in the New Testament? Other than the Didache, I see no explicit support for triune immersion from the writings from the first and second century. Tertullian speaks of thrice immersions as being "an ampler pledge" than what is found in Scripture. Ampler means greater. Therefore, he is saying that triune immersion is somewhat greater than what Jesus described in Matthew 28, and therefore something beyond what Christ commanded."
There is no explicit mention in the New Testament of either single or triple immersion, and so we have to look beyond the New Testament for answers here. You say "other than the Didache", as if the fact that the Didache does mention this is a small matter. The Didache is the earliest Christian writing that is not part of the New Testament, and was highly regarded in the early Church, as can be seen by its mention in St. Athanasius' famous Paschal Epistle of 367, in which he provides the earliest complete list of the New Testament canon, as the Church has received it. Most of the writings that we have from the second century are Apologetic writings, directed towards those outside of the Church. The internal teachings of the Church were still intentional left unwritten, until the time that the persecutions in the Roman Empire ceased.
The comment that you mention from Tertullian dates from about 204 a.d., and is found in his treatise "De Corona", chapter 3:
"And how long shall we draw the saw to and fro through this line, when we have an ancient practice, which by anticipation has made for us the state, i.e., of the question? If no passage of Scripture has prescribed it, assuredly custom, which without doubt flowed from tradition, has confirmed it. For how can anything come into use, if it has not first been handed down? Even in pleading tradition, written authority, you say, must be demanded. Let us inquire, therefore, whether tradition, unless it be written, should not be admitted. Certainly we shall say that it ought not to be admitted, if no cases of other practices which, without any written instrument, we maintain on the ground of tradition alone, and the countenance thereafter of custom, affords us any precedent. To deal with this matter briefly, I shall begin with baptism. When we are going to enter the water, but a little before, in the presence of the congregation and under the hand of the president, we solemnly profess that we disown the devil, and his pomp, and his angels. Hereupon we are thrice immersed, making a somewhat ampler pledge than the Lord has appointed in the Gospel."
First, it should be noted that Tertullian was not writing to convince anyone that Christians should be baptized by a triple immersion -- he is arguing another point, based on Church Tradition, and cites this as an example of Church Tradition that is not found explicitly in Scripture, but which no one disputed.
Furthermore, when he speaks of the person "making a somewhat ampler pledge than the Lord has appointed in the Gospel," he is not referring to the triple immersion... because that is not a "pledge." A "pledge" is a solemn promise, and Tertullian simply notes that there are a number of promises made at baptism that you will not find explicitly required of a person being baptized in Gospels.
St. Basil the Great makes an almost identical argument in his treatise on the Holy Spirit, in which he argues that the Holy Spirit is a Person, and cites the doxology "Glory to the Father, and to the Son, and to the Holy Spirit. now and ever and unto the ages of ages. Amen." in support of that argument. He counters the objection that the doxology, though an ancient part of the universal liturgical tradition of the Church, is not found in Scripture by saying:
"Of the beliefs and practices whether generally accepted or publicly enjoined which are preserved in the Church some we possess derived from written teaching; others we have received delivered to us "in a mystery" by the tradition of the apostles; and both of these in relation to true religion have the same force. And these no one will gainsay; — no one, at all events, who is even moderately versed in the institutions of the Church. For were we to attempt to reject such customs as have no written authority, on the ground that the importance they possess is small, we should unintentionally injure the Gospel in its very vitals; or, rather, should make our public definition a mere phrase and nothing more. For instance, to take the first and most general example, who is thence who has taught us in writing to sign with the sign of the cross those who have trusted in the name of our Lord Jesus Christ? What writing has taught us to turn to the East at the prayer? Which of the saints has left us in writing the words of the invocation at the displaying of the bread of the Eucharist and the cup of blessing? For we are not, as is well known, content with what the apostle or the Gospel has recorded, but both in preface and conclusion we add other words as being of great importance to the validity of the ministry, and these we derive from unwritten teaching. Moreover we bless the water of baptism and the oil of the chrism, and besides this the catechumen who is being baptized. On what written authority do we do this? Is not our authority silent and mystical tradition? Nay, by what written word is the anointing of oil itself taught? And whence comes the custom of baptizing thrice [i.e., by triple immersion]? And as to the other customs of baptism from what Scripture do we derive the renunciation of Satan and his angels? Does not this come from that unpublished and secret teaching which our fathers guarded in a silence out of the reach of curious meddling and inquisitive investigation? Well had they learnt the lesson that the awful dignity of the mysteries is best preserved by silence. What the uninitiated are not even allowed: to look at was hardly likely to be publicly paraded about in written documents. What was the meaning of the mighty Moses in not making all the parts of the tabernacle open to every one? The profane he stationed without the sacred barriers; the first courts he conceded to the purer; the Levites alone he judged worthy of being servants of the Deity; sacrifices and burnt offerings and the rest of the priestly functions he allotted to the priests; one chosen out of all he admitted to the shrine, and even this one not always but on only one day in the year, and of this one day a time was fixed for his entry so that he might gaze on the Holy of Holies amazed at the strangeness and novelty of the sight" (Treatise on the Holy Spirit, 66).
Again, St. Basil is not trying to convince anyone that Christians should be baptized by a triple immersion -- he is appealing to the fact that everyone accepts this unwritten tradition to argue for authority of another unwritten tradition: the doxology. And one has to ask, how did this universally accepted Christian Tradition come to be universally accepted, if it did not come from the Apostles themselves? However, the bottom line here is the question of the authority of the Church. If you accept that the Orthodox Church is what it claims to be -- the one, holy, Catholic, and apostolic Church established by Christ, then questions like this are easily answered.
I would suggest you read my essay "Sola Scriptura: In the Vanity of Their Minds," and St. Cyprian of Carthage's treatise "On the Unity of the Church."
