Not necessarily. The Roman Catholic Magisterium continues to teach and to clarify the truths found in the Sacred Deposit of Faith (Tradition and Scripture). Any new development of doctrine and any magisterial teachings issued subsequent to the time of that Saint are incumbent upon you. The Saints and Doctors and Fathers of the Church are not infallible.
All the faithful are required to adhere, with the full assent of faith, to every infallible doctrine of the Magisterium. If an infallible doctrine is issued subsequent to the time of any Saint, we cannot expect that Saint to have anticipated the future teaching and infallible definition of the Magisterium. Or, to put it another way, if that Saint were living today, he or she would surely adhere to every infallible teaching of the Church, even if it required that Saint to change his or her opinion. The theological opinions of the Saints are not dogma, and they are not presented by the Saints as if they were dogma.
Example: Saint Thomas Aquinas expressed an incorrect opinion on the conception of the Virgin Mary in the Summa Theologica. Many years after his death, the Magisterium began to teach, first non-infallibly, and later infallibly, the correct doctrine on the Immaculate Conception. Can a Catholic today hold the opinion of St. Thomas on the conception of Mary? Not at all. To do so would be abject heresy. If St. Thomas was living today, would he still hold the same incorrect opinion on that subject? Certainly not. He would change his opinion to agree with the teaching of the Church.
So then, if you know that a Saint held a particular theological opinion, and you favor that opinion, thinking it to be true, you must nevertheless change your mind and heart on the subject, if the Magisterium teaches otherwise. Whenever we read a theological opinion of a Saint, we must not treat it as a dogma. We are required by our faith in the Church to seek the teaching of the Magisterium on that topic also, especially teachings more recent than the life of that Saint, before we decide what to believe.
We are also obligated to give the religious submission of will and intellect to the non-infallible doctrines of the Magisterium. One cannot simply ignore or contradict a non-infallible teaching on the basis that a Saint once held a contrary view. There is NO OBLIGATION in the faith to hold a particular theological opinion, merely because Saint Thomas, or some other Saint, Doctor, or Father of the Church, held that opinion. But we are obligated to give religious assent (ordinary assent) to non-infallible teachings, and the full assent of faith (sacred assent) to the infallible teachings of the Magisterium.
No Saint, Father, or Doctor of the Church would approve of anyone adhering to his or her saintly theological opinion, in contradiction to a teaching of the Magisterium, even if that teaching were non-infallible.
So, for example, when the Catechism of the Catholic Church teaches that lying is by its nature wrong (and therefore intrinsically evil) and that all intrinsically evil are always immoral, regardless of intention or circumstances, we are required to believe that teaching. Recourse to the past opinion of a Saint cannot justify rejecting the non-infallible teaching that lying is intrinsically evil, nor the infallible teaching (under the ordinary and universal Magisterium) that intrinsically evil acts are always immoral, independent of intention or circumstances.
And the same is true for past sources of less weight than the opinion of a Saint. If an older book has the imprimatur, and yet it contains a theological opinion that contradicts a later teaching of the Magisterium, you cannot use the opinion of that book and its imprimatur to justify rejecting the current teaching of the Church.
The Magisterium teaches that lying is intrinsically evil and therefore always immoral, no matter what the intention or circumstances. This is a required belief, at least under the ordinary Magisterium, to which we must give the religious submission of will and intellect.
However, the vast majority of Catholics today give more weight to their own ideas, feelings, and passing thoughts than to any teaching of the Magisterium. Truly, the great apostasy is near, at the very threshold.
by
Ronald L. Conte Jr.
Roman Catholic theologian and
translator of the Catholic Public Domain Version of the Bible.
the reproach of Christ 
Since an atheist doesn’t by definition doesn’t believe in God I find it hard to see how we can have common ground with them.
The common ground can be love of neighbor.
How about when a Pope declares that atheists can be good and we can find common ground with them? Are we permitted to hold that view?
We are permitted to hold any view that does not contradict a doctrine. The Pope’s recent comment about atheists in a sermon does not fall under the Magisterium. But I see nothing wrong with what he said.
The teachings of a canonized saint who was a Pope of the Catholic Church can sometimes fall under papal infallibility or conciliar infallibility, but not every teaching of a canonized saint who was a Pope is infallible. Furthermore, the teaching of a canonized saint who was a bishop of the Catholic Church can sometimes be infallible under conciliar infallibility or the ordinary and universal Magisterium, but not every teaching of a canonized saint who was a bishop of the Catholic Church is infallible. Every teaching or theological opinion that does not fall under any of the three modes of infallibility, including those of Fathers, Doctors, and Saints, are not infallible.
If an idea is taught by a Pope as an act of the Magisterium, then it is irrelevant if the Pope is canonized. Magisterial teachings from Saints don’t have higher authority than Magisterial teachings from non-Saints.