God holds eternal life out to us upon a condition (John 3:16). If we believe in Christ, we will be saved. If we do not believe in Christ, we will not receive what is offered, and we will perish.
While the gospel is not conditional as respects any merit or power in us (contrary to Arminianism), yet it is equally wrong to say with hyper-calvinists that the gospel has no conditions whatsoever. Samuel Rutherford (a Westminster divine) here exposits (in congruity with the Westmisnter Larger Catechism #32) how the gospel has evangelical conditions, without which we will never see the Lord (Heb. 12:14).
Rutherford, Samuel – The Gospel is Conditional 1648, 3 pages, being Part 2, Chapter 38, pp. 39-40 of his A Survey of the Spiritual Antichrist.