"Therefore, forasmuch as no man is excluded from calling upon God, the gate of salvation is set open unto all men; neither is there any other thing which keepeth us back from entering in, save only our own unbelief" - John Calvin, Commentary of the Acts of the apostles 2:21

Those in the reformed community have always believed that the outward call of the gospel goes out to all people who hear without exception, but sadly they all resist this outward call, not because God coerces them, but because of their own stubborn unbelief. So the gates are open for all who want to come in but apart from the Holy Spirit, no one does. We declare to the world, "trust in Jesus Christ and you will be saved." But men love darkness and hate the light and will not come into the light (John 3:19-20). Man is stiff necked and will not come yet amazingly God IS STILL merciful. Through the call of the gospel He extends mercy to more ill-deserving sinners than any man can count in spite of themselves. If he left us to our own so called "free will" then no one would be saved since we all willfully run the other way... left to our own devices, we would all be hopelessly lost. Jesus declared, "the Spirit quickens, the flesh counts for nothing...that is why I told you that no one can come to me unless the Father who sent me grants it." John 6:63, 65.

Calvin himself said the following

"...we allow that man has choice and that it is self-determined, so that if he does anything evil, it should be imputed to him and to his own voluntary choosing. We do away with coercion and force, because this contradicts the nature of the will and cannot coexist with it. We deny that choice is free, because through man's innate wickedness it is of necessity driven to what is evil and cannot seek anything but evil. And from this it is possible to deduce what a great difference there is between necessity and coercion. For we do not say that man is dragged unwillingly into sinning, but that because his will is corrupt he is held captive under the yoke of sin and therefore of necessity will in an evil way. For where there is bondage, there is necessity. But it makes a great difference whether the bondage is voluntary or coerced. We locate the necessity to sin precisely in corruption of the will, from which follows that it is self-determined." - John Calvin from Bondage and Liberation of the Will, pg. 69-70

"... we preach Christ crucified: a stumbling block to Jews and foolishness to Gentiles,  but to those whom God has called, both Jews and Greeks, Christ the power of God and the wisdom of God." 1 Cor 1:23-24

-----

Related Resources
The Gospel Call & The Effectual Call by Anthony A. Hoekema
The Universal Proclamation of the Gospel & The Particular Call of Grace by Herman Bavinck
The Necessity of Word & Spirit in Conversion by John Calvin