Certainly,The 7th canon of the Council of Neocaesarea (c. 315) speaks of second marriages. They are undesirable, as the pre-schism church desires lifelong marriage, but it realized this was both impractical and at times impossible. It also recognizes a need for mercy because the couple is “worthy of penance” and should be given an indulgence to continue.
For the benefit of the readers, the 7th canon reads as follows:
*"Canon 7
A presbyter shall not be a guest at the nuptials of persons contracting a second marriage; for, since the digamist is worthy of penance, what kind of a presbyter shall he be, who, by being present at the feast, sanctioned the marriage?*
As you have acknowledged, this canon clearly speaks against the second marriage after the first ends in divorce (there has never been a prohibition against marrying after the death of the first spouse).
That
“the digamist is worthy of penance” means that he is in sin which is why the presbyter cannot sanction the marriage. You have misread the canon.
The Church’s mission on earth is to administer the mercy of God. That is what penance is all about. But mercy does not mean that the Church sanctions what is unholy. It means calling the person back to fidelity with God by requiring a renunciation of one’s sin and a true intention to not continue in that sin. This is done in the sacrament of Reconciliation.
The Church has never changed its stance concerning a valid marriage. If one divorces and marries again they commit adultery. The question comes down to whether or not the marriage was valid to begin with. If it is valid then we believe that it is impossible for any human to break the sacramental and indissoluble bond of marriage: * "therefore, let no one separate what God has joined”* (Mt. 19:6). That is where the annulment process comes into play. There are certain situations where there never was a valid marriage to being with. The Church carefully weighs the evidence based upon certain factors.
The following is a good summation of the Church’s view of marriage, taken from the Archdiocese of Atlanta Metropolitan Tribunal:
*"A number of elements must come together for the sacrament of marriage to occur. The first is the “Canonical Form” of marriage: a Catholic must ordinarily be married within a Catholic church and before a priest or deacon. The requirements for the Canonical Form of marriage applies only to Catholic spouses, so we would recognize the marriage of two persons who are not Catholic, even if they did not marry in a church ceremony or religious service.
However, following the proper canonical form of marriage is not all that is necessary for a valid sacramental marriage to take place. The couple must also freely and knowingly choose to enter marriage as the Church understands marriage. This is “Marital Consent.” A number of intentions must be made by the couple at the time of marriage in order for consent to be valid, that is, in order to establish the unbreakable bond between husband and wife that is a sacramental marriage. The couple must understand what marriage is and they must intend their marriage to be a lifelong partnership which is open to children. They must intend fidelity and the mutual good of one another. They must also have the physical and psychological ability to follow through on these intentions.
When all of the above factors are brought together, a sacramental, indissoluble union is established by God. If a Catholic spouse marries with the proper Canonical Form and with at least the semblance of the necessary intentions given through the marriage vows, we recognize the enduring marriage bond which cannot be dissolved, even if the civil government, through divorce, no longer recognizes that a marriage exists."*
The point is that the Church has never changed its doctrine concerning the sacramental nature of marriage and its indissolubility. I think there has certainly been some progress made in how the Church handles individual cases but the doctrinal basis on which these decisions are made have never changed.