from an article by J.I. Packer here.
Biblically, the difference between these two conceptions of how God in love relates to fallen human beings may be pinpointed thus. Arminianism treats our Lord’s parable of the Supper to which further guests were invited in place of those who never came (Luke 14:16-24; cf. Matt. 22:1-10) as picturing the whole truth about the love of God in the gospel. On this view, when you have compared God’s relation to fallen men with that of a dignitary who invites all needy folk around to come and enjoy his bounty, you have said it all. Calvinism, however, does not stop here, but links with the picture of the Supper that of the Shepherd (John 10:11-18, 24-29) who has his sheep given him to care for (vv. 14, 16, 27; cf. 6:37-40; 17:6, 11f.), who lays down his life for them (10:15), who guarantees that all of them will in due course hear his voice (vv. 16, 27) and follow him (v. 27), and be kept from perishing forever (v. 28). In other words, Calvinism holds that divine love does not stop short at graciously inviting, but that the triune God takes gracious action to ensure that the elect respond. On this view, both the Christ who saves and the faith which receives him as Savior are God’s gifts, and the latter is as much a foreordained reality as is the former. Arminians praise God for providing a Savior to whom all may come for life; Calvinists do that too, and then go on to praise God for actually bringing them to the Savior’s feet.
So the basic difference between the two positions is not, as is sometimes thought, that Arminianism follows Scripture while Calvinism follows logic, nor that Arminianism knows the love of God while Calvinism knows only his power, nor that Arminianism affirms a connection between believing and obeying as a means and eternal life as an end which Calvinism denies, nor that Arminianism discerns a bona fide “free offer” of Christ in the gospel which Calvinism does not discern, nor that Arminianism acknowledges human responsibility before God and requires holy endeavor in the Christian life while Calvinism does not. No; the difference is that Calvinism recognizes a dimension of the saving love of God which Arminianism misses, namely God’s sovereignty in bringing to faith and keeping in faith all who are actually saved. Arminianism gives Christians much to thank God for, and Calvinism gives them more.