One of my 'must have on the shelf' would be the letters of John Newton. Here is a great quote:
“The message I would bear is Jesus Christ and him crucified and from the consideration of the great things he has done, to recommend and enforce Gospel holiness and Gospel love, and to take as little notice of our fierce contests, controversies and divisions as possible.
My desire is to lift up the banner of the Lord, and to draw the sword of the Spirit not against names, parties and opinions, but against the world, the flesh and the devil; and to invite poor perishing sinners not to espouse a system of my own or any man’s, but to fly to the Lord Jesus, the sure and only city of refuge and the ready, compassionate and all sufficient Saviour of those that trust in him.”
(h/t J Taylor)