If Jesus Christ should allow us once to think that [the sinner who comes to him] shall be cast out, then he must allow us to question his will, or power, or merit to save. But he cannot allow us once to question any of these – therefore, not once to think that the coming sinner shall be cast out.
1. He cannot allow us to question his will; for he says in the text, ‘I will in no wise cast out.’
2. He cannot allow us to question his power; for the Holy Ghost says, he is able to save to the uttermost them that come.
3. He cannot allow us to question the efficacy of his merit: for the blood of Christ cleanses the comer from all sin, 1 John 1.
This is John Bunyan writing about the statement of the Saviour, ‘Him that cometh to me I will in no wise cast out.’ John 6: 37.
He wrote a whole book devoted to this one verse. In it he explores not only our need of a Saviour but also the perfect suitability of the Saviour who God has provided for that need. And he demonstrates beyond all possible doubt that needy sinners are welcome to come to this Saviour Jesus Christ. The statement is a promise made by God the Son: it is totally dependable truth, and it’s presented to us so that we would, in fact, depend on it.
John Bunyan, Come and Welcome to Jesus Christ: A Plain and Profitable Discourse on John 6: 37. First published 1681, my edition 1820, p192