Paul begins each of his epistles with a greeting. Many of these greetings are positive. He rejoices that they are saved and growing.
In most cases where he rejoices in their faith, he says he knows their faith because he observes one huge trait among them: love.
“I heard of your faith in the Lord Jesus, and love unto all the saints” Ephesians 1:15
“we heard of your faith in Christ Jesus, and of the love which ye have to all the saints” Colossians 1:4
“Remembering without ceasing your work of faith, and labour of love” 1 Thessalonians 1:3
“your faith groweth exceedingly, and the love of every one of you all toward each other aboundeth” 2 Thessalonians 1:3
“Hearing of thy love and faith” Philemon 5
Almost makes a guy wonder if there is a consistent biblical proof of genuine faith, eh?
Seems to me there is. You know there is true faith when you love the Lord your God and love your neighbor as yourself. Love is the fulfilling of the Law. Love is what was on display at the cross. It’s all about love, because God is love.