Is a Christian’s faith a purely private affair?

I hear some people say that their faith is personal and private and not subject to scrutiny. I hear some people say “That person has publicly confessed Jesus as Lord and Savior. How can I judge otherwise?”
While a person’s relationship with God is personal, it’s not strictly private. If someone is in relationship with God, it will show in their life.
In Paul’s Epistle to the Galatians, we find this teaching:
“But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control; against such things there is no law.”
The Spirit mentioned here is the Holy Spirit. Paul admonishes his readers to “walk by the Spirit.” If someone is walking by the Spirit, they will start to show the fruit of the Spirit in their life. They may not change instantaneously; following God always is a work in progress. But over time, the person will be changed for good by the Holy Spirit.
It’s like if someone has a house and told me that they have a fire in the fireplace. I may not be able to look into the house, but if there really is a fire, I should be able to see smoke from the chimney. As Jesus says in the Gospel of Luke:
“For no good tree bears bad fruit, nor again does a bad tree bear good fruit, for each tree is known by its own fruit…The good person out of the good treasure of his heart produces good, and the evil person out of his evil treasure produces evil, for out of the abundance of the heart his mouth speaks.”
The fruit of the Holy Spirit is a public expression for a Christian’s personal walk with God. A person can claim to be a Christian. They can attend worship services. They can post about faith on social media. They can take pictures of themselves holding a Bible or kneeling at an altar. But if they are not demonstrating the fruit of the Spirit, it’s like claiming to have a fire with no smoke. After a while, I would wonder if the fire is even there in the first place.
For my part, this teaching is a reminder to continue to cultivate the fruit of the Spirit by walking with the Spirit. As Paul writes in Galatians, “If we live by the Spirit, let us also keep in step with the Spirit. Let us not become conceited, provoking one another, envying one another.”