When I was a child we sang a lyric, “faith is like a muscle, use it and it will grow”. How do you know your faith muscle is growing? Because you “use it”, the song says.
Faith grows through challenges. We experience how faith in God brings comfort, peace, wisdom, strength. Challenges might come because of loss, sickness, estrangement, sin. This is the ‘dark’ side of challenge. We are squashed because bad things are happening. The ‘light’ side of challenge are where good things are happening and it stretches us. We get a new job, enter a new relationship, have a child, help someone out. How often is our faith pushed because of the ‘dark’, rather than the ‘light’ side of challenge?
I think the kind of suffering addressed in the New Testament is that of the ‘light’ side. Christians are challenged as following Jesus results in real hardship. Their faith is stretched. When you suffer for a meaningful reason, it is easier to see what it is achieving. Hence Peter can write to persecuted Christians regarding their suffering, “These have come so that the proven genuineness of your faith—of greater worth than gold, which perishes even though refined by fire—may result in praise, glory and honour when Jesus Christ is revealed. (1 Peter 1:7).
We can grow our faith by stretching ourselves more. We can place ourselves in opportunities which mean we must rely more on God. This might include discipling someone, leading a growth group, taking up pastoral care, serious prayer ministry, ministry leadership, evangelism…who knows what will stretch you? All I know is to grow faith, you must use it.