Durham’s exceedingly rich and valuable collection of sermons, ‘The Unsearchable Riches of Christ’ is nowhere on the internet and often goes for quite a price on the used book market.  For those that do not have it, here is:

Durham’s ‘The Unsearchable Riches of Christ’ on the Sincere Free Offer of the Gospel

Notice Durham’s language of purpose and intention, that the purpose and intention of God in offering salvation in Christ to gospel hearers is so that they would take it.