According to Paul Helm (Highland Theological College):
‘Definite atonement’ is an improvement on ‘Limited atonement’, but neither phrase clearly captures and expresses the idea, which is not exclusively to do with the atonement. The view is that the Triune God ensures the salvation of men and women, boys and girls. He does not merely make possible their salvation, leaving it to the sinner to make up his own mind. Rather, whom he intends to save, he saves, through the distinct but inseparable work of Father, Son and Holy Spirit. As Augustine puts it in his letter to Simplicianus in AD 396, God’s grace is effectual, effective, actually ensuring that those ordained to eternal life believe, secured by the golden chain of Romans 8.
What is at issue is an estimate of divine grace. The biblical basis for the view does not rest upon a single proof verse, or a few of these, (though verses such as John 6.37 and Acts 13.48 and of course Romans 8 28f should be borne in mind). Rather it is founded on the implications of Scripture’s overall witness to God’s powerful love, to the spiritual death of fallen mankind, and to the actual salvation of countless people.