The reason I brought up existentialism is to emphasize how quickly a way of thinking can grow into a complicated and disparate muddle of often contradictory viewpoints. The simple defining thoughts are lost. The author of the essay we are talking about, I believe, was trying to simplify the Biblical perspective from the disparate, confusing muddle of viewpoints Christianity has become. Perhaps his efforts were too simple.
However, the Gospel message is simple and direct: "God exists, and He rewards those who earnestly seek Him."
A problem arises when we get intellectually lost in that muddle which I mentioned. (By the way, I used EncyclopediaBritannica.com for my research on existentialism.)
Now, through experience, many have found that God really does exist and has changed their lives from the inside out. Their acceptance of Jesus' Gospel message has changed their lives dynamically from the inside out. It is not for show or hypocritical play acting - although I am aware that there are many posers in the world.
Unfortunately, many people do not accept our testimony. While people willingly accept the testimony of automobile manufacturers, ads testifying to beauty product miracles, schemes to get rich quick, and so on and so forth, former drug, tobacco, and alcohol addicts testifying to the miraculous rescue and beneficial changes in their lives are ignored or discredited. Yet, those changes in their lives are, at least, a partial definition of what can be considered "good."
God created everything, knows how everything works, and like good and insightful parents, knows what is best for us and what is dangerous and/or harmful for their children. So, God tries to instruct us in His ways and prevent us from harm. I think that is love. Beyond that, God has given us free will and the power of choice. That also is love.
No one, including you and I, cannot love someone without choosing to do so and without determining that they are good. We make that determination, whether or not it pans out. Nevertheless we choose what is the definition of "good."
God has provided us with a better definition.
I think if you read what has been recorded in the Bible as in the Sermon on the Mount in Matthew, chapters 5, 6, and 7, you would have a hard course to run to conclude that God is not righteous and good, or that "good" cannot be defined.