NOT ALL Christians follow the basic Nicene Creed because they deny one line of the Creed,
"We affirm one baptism for the forgiveness of sins."
Here's why.
Look at that line, is this what Baptists, Reformed and Evangelicals think about Baptism?
No. Many of them will say "it's just a symbol" or "it's done after you are saved as a public declaration of faith". So by this plain reason alone not all Christians follow this Creed.
A Baptist might say "But that creed simply means Baptism as a SYMBOL of that forgiveness".
Well no this is not true just by virtue of looking at how some Nicene theologians view Baptism. Let's start with the champion of Nicaea, Athanasius
when baptism is given, whom the Father baptizes, him the Son baptizes; and whom the Son baptizes, he is consecrated in the Holy Ghost. And again as when the sun shines, one might say that the radiance illuminates, for the light is one and indivisible, nor can be detached, so where the Father is or is named, there plainly is the Son also; and is the Father named in Baptism? Then must the Son be named with Him.-Disclosures against the Arians, 2.18.41
The faith in the Trinity transmitted to us is the only one, and it unites us with God, and whoever takes something away from the Trinity and baptizes in the name of the Father, or in the Son alone, or into the Father and the Son without the Spirit, receives nothing, but those being baptized and he imagines himself to be giving baptism remain in vanity and unconsecrated, because the Mystery is accomplished in the name of the Trinity: so that whoever seperates the Son from the Father or reduces the Spirit to a creature has neither the Son nor the Father but is an atheist, worse than an unbeliever, and anything but a Christian. (Epistle to Serapion 1.30)
Here, two ideas of Baptism can be gleaned, first there is a Triune action by the Godhead going on and a consecration of the one Baptized to the Holy Spirit. Those who receive it are also united with God. Can Baptists claim as Athanasius does?
Of course not.
Next consider St. Basil the Great (329-379). In the tenth chapter of his De Spiritu Sancto (On the Holy Spirit) he writes:
Whence is it that we are Christians? Through our faith, would be the universal answer. And in what way are we saved? Plainly because we were regenerate through the grace given in our baptism. How else could we be? And after recognising that this salvation is established through the Father and the Son and the Holy Ghost, shall we fling away “that form of doctrine” (Romans 6:17) which we received? Would it not rather be ground for great groaning if we are found now further off from our salvation “than when we first believed,” and deny now what we then received? …. For if to me my baptism was the beginning of life, and that day of regeneration the first of days, it is plain that the utterance uttered in the grace of adoption was the most honourable of all. Can I then, perverted by these men’s seductive words, abandon the tradition which guided me to the light, which bestowed on me the boon of the knowledge of God, whereby I, so long a foe by reason of sin, was made a child of God? But, for myself, I pray that with this confession I may depart hence to the Lord, and them I charge to preserve the faith secure until the day of Christ, and to keep the Spirit undivided from the Father and the Son, preserving, both in the confession of faith and in the doxology, the doctrine taught them at their baptism. (Chapter 10)