Where to Start?
The best place to start is with the Scriptures. The Sincere Free Offer of the Gospel forms no small part of the teaching of God’s Word:
Fentiman, Travis – Bible Verses on Common Grace and the Sincere Free Offer of the Gospel, 2014, 34 passages with commentary
Fentiman, Travis – John 3:16 – God’s Love for all Mankind in the Sincere Free Offer of the Gospel, 2014, 16 paragraphs
For two rich gospel sermons from Isaiah 55 sincerely offering the free Gospel to poor penny-less sinners, see:
Durham, James – The Unsearchable Riches of Christ, Buy mid-1600’s
The best medium length article on the topic, though it is dense, is by Adam Gib.
Gib, Adam – The Open Door of the House of Mercy, 1774, 7 pages
This is the best theological analysis of the Sincere Free Offer of the Gospel. Gib posits the grounds of the Sincere Free Offer in the Revealed Will of God, as opposed to the Decrees of God and the Extent of the Atonement. He distinguished and guards the doctrine from a General Atonement of the Arminians on the one hand, and relates it to Biblical Limited Atonement on the other hand. Gib was a mid-1700’s Scottish minister from the Seceder tradition.
For an all out Biblical and historic defense of the Sincere Free Offer of the Gospel, see the book by Rev. Silversides:
Siversides, David – The Free Offer: Biblical and Reformed, Buy 2005, 128 pages
This is the most extensive work defending the Biblical view of the Sincere Free Offer of the Gospel. It also includes a valuable, extensive anthology of excerpts from historic, reformed writers demonstrating that the Sincere Free Offer of the Gospel has always been a regular part of reformed gospel preaching.
Here is Ian H. Murray’s review of the book.
Fentiman, Travis – The Lord’s Feast, a Sermon on Isa 55:1,2, note that the sermon starts at about 20 seconds. Preached at a free, evangelistic Thanksgiving Feast.
Isa. 55:1 – “Ho, every one that thirsteth, come ye to the waters, and he that hath no money; come ye, buy, and eat; yea, come, buy wine and milk without money and without price.“