The first reading today includes the command,
Add nothing to his words, lest he reprove you, and you will be exposed as a deceiver.
And we Catholics still get accused of adding to the word of God. But a couple of things on that point.
Firstly, the reading is from Proverbs a book of the Old Testament. God later made a huge addition; we call it the New Testament.
Secondly, and much more important the Catholic Church teaches unequivocally that nothing can be added. In our prayer at each mass we speak of the "new and eternal covenant" it "will never pass away and we now await no further new public revelation before the glorious manifestation of our Lord Jesus Christ (see 1 Tim. 6:14 and Tit. 2:13)" The Bible with all its books is the final public revelation.
When we speak of doctrine we are not adding to but explaining what it there. As the catechism says, "Yet even if Revelation is already complete, it has not been made completely explicit; it remains for Christian faith gradually to grasp its full significance over the course of the centuries." Who would dare say they understand fully what is contained in the Bible?
As individuals we are called to read the Word of God and apply it to our lives daily. There is always the danger that we read what we want and we hear in the Word of God what we want to hear. We call prophetic those friends who tell us what we want to hear. We close our eyes and our ears to hard truth.
Jesus knew this about us and it is why when he created the Church he chose the apostles, establishing the apostolic office, creating what we now call the magisterium whose job it is to examine various interpretations of scripture to discern what is of God and what is merely some person's wishful thinking.
You may have noticed the phrase "public revelation" above in reference to the Bible. That is to distinguish it from "private revelation." While for us Christians the New Testament is the final word addressed to all and binding on all, God continues to speak to individuals. We call that private revelation. They may choose to share that with others.
The Church never says you must believe in those things. They are, after all, intended for the receiver. The most the Church ever does is examine the content and say that to believe this would do you know harm. About these private revelations the Church says, "It is not their role to improve or complete Christ’s definitive Revelation, but to help live more fully by it in a certain period of history."
In Catholic circles the most famous of these are the Marian apparitions at Fatima, Lourdes, etc, or St. Faustina quoting some of her conversations with Jesus. They are not part of what "we believe" they are aids to living the faith. In non-Catholic circles the devotional book Jesus Calling, might be seen as an example of private revelation, an individual sharing what she believes Jesus is saying to her.
Each day we should engage in both. Reading the public revelation, the Bible. And just as important opening our hearts to the intimately personal conversation with Jesus. The Sprit of God stands ready to speak of each of us, if we will only listen.