This is a question that people wrestle with, but I believe that you absolutely can measure spiritual growth.
You can't look into someone's heart to see if someone trusts God more, but I can look at the fruit in someone's life and see if they exhibit the signs of a person who trusts God.
Do they trust God for salvation?
Do they trust God and make decisions that are in accordance with the Scriptures?
Do they trust God with their finances?
Do they trust God to relinquish control?
So while I can't put a person up to a faith-o-meter to see if their faith is growing, I can look at a person's fruit to see if they exhibit the fruit of someone who is growing in faith.
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