Acts 18:26 English Standard Version (ESV) He began to speak boldly in the synagogue, but when Priscilla and Aquila heard him, they took him aside and explained to him the way of God more accurately.
We are blessed to live in a time when we have all of the New Testament to read. If we were to live in the 1st century church we might have to wait years for the next letter to be written by Paul and distributed throughout the region. That comment was not meant to persuade anyone away from reading the Old Testament. Please do not assume that position.
What is important is that during Paul’s imprisonment his epistles to the churches formed a series of exhortations on how the body of Christ should interact with one another. They are the foundation of exhortation in living with each other. Up until the time the bible was canonized Christians had to rely on each other and their personal relationship with God and in the power of the Holy Spirit. This is how Priscilla and Aquila could exhort Apollos.
In this sense exhortation is not admonishment as some would fear but rather to draw them into fellowship with those who have a better understanding of the Way. In Acts 18:3 it is noted that Paul came to live with Priscilla and Aquila because they were all tent makers. They learned the Way more accurately from Paul directly. They had no need for an epistle.
These devotionals and many others published daily are not epistles. They are exhortations of a type in which we share what we know and are led to write by the influence of the Holy Spirit. They are not intended to replace those epistles. Devotional writers encourage the reader to do personal bible reading. These are not meant to replace personal quiet time.
Go, read your bible.