Reformation Sunday is for celebrating not just one day memorializing an event 507 years ago. It is a celebration for every day because of our resurrected Jesus who is the truth we still stand on from Scripture alone.
The best way to get at the Gospel in our Amos reading is to connect it to Christ. It is too easy and tempting to associate it with social justice today. Our people will not need much encouragement to go there. What they need is the surprising and salvific connection to Christ
Jesus' active obedience is what saves you from your active sinning. He took your sin to the cross and that one act of obedience is what led to your justification by grace through faith on account of His glorious resurrection.
He is a God who changes curses into blessings. We see that clearest in Jesus, whose life, ministry, atoning death, and glorious resurrection is the Way, the Truth, and the Life.
It is the humble who will rejoice in the Holy One of Israel. Or, as Jesus said it elsewhere in Matthew: “The poor in spirit are blessed because theirs is the Kingdom of Heaven.”