This verse is a final encouragement from the Apostle Peter. He urges believers to keep growing spiritually:
We look into this in perspective of a baby teething, Just like a baby starts with milk but eventually grows teeth so they can eat more solid food, Christians are meant to grow in their spiritual lives too.
A teething baby is going through growth — sometimes uncomfortable, but necessary.
Peter is saying that believers shouldn't stay spiritual "babies" forever. We should grow stronger in understanding God's grace and knowing Jesus better.
Just like teething prepares a baby for more nourishment, growing in grace and knowledge prepares a Christian for a deeper, stronger walk with God.