The pagans struggle believing in one God, and see the three persons as three gods

The simple, indeed, (I will not call them unwise and unlearned,) who always constitute the majority of believers, are startled at the dispensation (of the Three in One), on the ground that their very rule of faith withdraws them from the world’s plurality of gods to the one only true God; not understanding that, although He is the one only God, He must yet be believed in with His own οἰκονομία . The numerical order and distribution of the Trinity they assume to be a division of the Unity; whereas the Unity which derives the Trinity out of its own self is so far from being destroyed, that it is actually supported by it.

Tertullian
Against Praxeas
Chapter III

The Trinity is one God in substance but three persons

But keeping this prescriptive rule inviolate, still some opportunity must be given for reviewing (the statements of heretics), with a view to the instruction and protection of divers persons; were it only that it may not seem that each perversion of the truth is condemned without examination, and simply prejudged; especially in the case of this heresy, which supposes itself to possess the pure truth, in thinking that one cannot believe in One Only God in any other way than by saying that the Father, the Son, and the Holy Ghost are the very selfsame Person. As if in this way also one were not All, in that All are of One, by unity (that is) of substance; while the mystery of the dispensation is still guarded, which distributes the Unity into a Trinity, placing in their order the three Persons—the Father, the Son, and the Holy Ghost: three, however, not in condition, but in degree; not in substance, but in form; not in power, but in aspect; yet of one substance, and of one condition, and of one power, inasmuch as He is one God, from whom these degrees and forms and aspects are reckoned, under the name of the Father, and of the Son, and of the Holy Ghost. How they are susceptible of number without division, will be shown as our treatise proceeds.

Tertullian
Against Praxeas
Chapter II

A summation of the orthodox faith

We, however, as we indeed always have done (and more especially since we have been better instructed by the Paraclete, who leads men indeed into all truth), believe that there is one only God, but under the following dispensation, or οἰκονομία , as it is called, that this one only God has also a Son, His Word, who proceeded from Himself, by whom all things were made, and without whom nothing was made. Him we believe to have been sent by the Father into the Virgin, and to have been born of her—being both Man and God, the Son of Man and the Son of God, and to have been called by the name of Jesus Christ; we believe Him to have suffered, died, and been buried, according to the Scriptures, and, after He had been raised again by the Father and taken back to heaven, to be sitting at the right hand of the Father, and that He will come to judge the quick and the dead; who sent also from heaven from the Father, according to His own promise, the Holy Ghost, the Paraclete, the sanctifier of the faith of those who believe in the Father, and in the Son, and in the Holy Ghost. That this rule of faith has come down to us from the beginning of the gospel, even before any of the older heretics, much more before Praxeas, a pretender of yesterday, will be apparent both from the lateness of date which marks all heresies, and also from the absolutely novel character of our new-fangled Praxeas.

Tertullian
Against Praxeas
Chapter I

Being both God and man united is what makes Christ the mediator between them

And so the flesh shall rise again, wholly in every man, in its own identity, in its absolute integrity. Wherever it may be, it is in safe keeping in God’s presence, through that most faithful “Mediator between God and man, (the man) Jesus Christ,” who shall reconcile both God to man, and man to God; the spirit to the flesh, and the flesh to the spirit. Both natures has He already united in His own self; He has fitted them together as bride and bridegroom in the reciprocal bond of wedded life.

Tertullian 
On the Resurrection of the Flesh
Chapter LXIII

Christians fast and remain virgins as a longing for the greater things experienced in heaven hereafter

We even, as we may be able, excuse our mouths from food, and withdraw our sexes from union. How many voluntary eunuchs are there! How many virgins espoused to Christ! How many, both of men and women, whom nature has made sterile, with a structure which cannot procreate! Now, if even here on earth both the functions and the pleasures of our members may be suspended, with an intermission which, like the dispensation itself, can only be a temporary one, and yet man’s safety is nevertheless unimpaired, how much more, when his salvation is secure, and especially in an eternal dispensation, shall we not cease to desire those things, for which, even here below, we are not unaccustomed to check our longings!

Tertullian
On the Resurrection of the Flesh
Chapter LXI

Our resurrected bodies can feel suffering, but can also overcome it

Thus our flesh shall remain even after the resurrection—so far indeed susceptible of suffering, as it is the flesh, and the same flesh too; but at the same time impassible, inasmuch as it has been liberated by the Lord for the very end and purpose of being no longer capable of enduring suffering.

Tertullian
On the Resurrection of the Flesh
Chapter LVII

If God only raises the soul then he really doesn’t raise the dead

If God raises not men entire, He raises not the dead. For what dead man is entire, although he dies entire? Who is without hurt, that is without life? What body is uninjured, when it is dead, when it is cold, when it is ghastly, when it is stiff, when it is a corpse? When is a man more infirm, than when he is entirely infirm? When more palsied, than when quite motionless? Thus, for a dead man to be raised again, amounts to nothing short of his being restored to his entire condition,—lest he, forsooth, be still dead in that part in which he has not risen again. God is quite able to re-make what He once made.

Tertullian
On the Resurrection of the Flesh
Chapter LVII

Both body and soul reap the reward or condemnation in the resurrection

For how absurd, and in truth how unjust, and in both respects how unworthy of God, for one substance to do the work, and another to reap the reward:  that this flesh of ours should be torn by martyrdom, and another wear the crown; or, on the other hand, that this flesh of ours should wallow in uncleanness, and another receive the condemnation!

Tertullian
On the Resurrection of the Flesh
Chapter LVI

Moses and Elijah’s appearing to Christ prove a resurrection of the of body

In that same scene Moses also and Elias gave proof that the same condition of bodily existence may continue even in glory—the one in the likeness of a flesh which he had not yet recovered, the other in the reality of one which he had not yet put off.

…So likewise changes, conversions and reformations will necessarily take place to bring about the resurrection, but the substance of the flesh will still be preserved safe.

Tertullian
On the Resurrection of the Flesh
Chapter LV

The same flesh that died is raised, otherwise the example of the seed makes no sense

Let us now see in what body he asserts that the dead will come. And with a felicitous sally he proceeds at once to illustrate the point, as if an objector had plied him with some such question.  “Thou fool,” says he, “that which thou sowest is not quickened, except it die.” From this example of the seed it is then evident that no other flesh is quickened than that which shall have undergone death, and therefore all the rest of the question will become clear enough. For nothing which is incompatible with the idea suggested by the example can possibly be understood; nor from the clause which follows, “That which thou sowest, thou sowest not the body which shall be,” are you permitted to suppose that in the resurrection a different body is to arise from that which is sown in death.  Otherwise you have run away from the example.

…Cleave firmly then to the example, and keep it well in view, as a mirror of what happens to the flesh: believe that the very same flesh which was once sown in death will bear fruit in resurrection-life—the same in essence, only more full and perfect; not another, although reappearing in another form.

Tertullian
On the Resurrection of the Flesh
Chapter LII