So, the free gift of God is purely because God chooses to give that gift to those to whom he wills. And, according to the Bible, He willed that gift before the foundation of the world.
By God's Mercy.
BEHOLD!; a secondary source:
Predestination
"Position 3.
This determinate plan existed from all eternity.
This follows from the infinite perfections of His nature— from His immutability. If He has a plan in time which He had not in eternity, then His mind has undergone a change. But, He says: I am the Lord—I change not (Mal. 3:6). He is the same yesterday, today, and forever, without variableness or shadow of turning—from His infinite knowledge.
If a plan exists in the Divine Mind, it is designed either to produce the occurrences in time or to meet them: either it is the cause of events or is caused by them. Upon either supposition, it existed from eternity.
Though it be granted that it was devised to meet the events that occur, in time, it must have existed from eternity; since those events are as fully comprehended in the divine knowledge from eternity as after their occurrence in time. Known unto God are all His works from the beginnings...
Let these premises be granted (and we see not how they can be denied) and Predestination comes in like a flood.
Now, God’s eternal decree, by which He makes all things in time fixed and sure, is nothing but His eternal plan, by which He governs Himself in His relations towards His creatures. And His works of providence and of grace are but the revealment of that eternal plan and, consequently, of His eternal purpose.
Is it true that the elements and all inanimate nature are controlled by Him? Then all their conditions and mutations are foreordained by Him before the beginning of time.
Is it true that He rules with as sovereign sway in the moral as in the physical world?—That the hearts of all men are in His hands and that He turns them as the rivers of water are turned?—
Does He send His Spirit, to a certain number and no more and convince them of sin, of righteousness, and of judgment? Call them effectually by His grace, regenerate, sanctify, and save them?
And does He do all this in accordance with a plan entertained from eternity?
Then it follows that they were predestined to this grace according to the purpose of Him who worketh all things alter the counsel of His own will.
Has moral evil entered into His system, and do wicked men sin against Him, he not paralyzing their faculties nor changing their hearts?
And does He leave some, as vessels of wrath, to hardness of heart and blindness of mind that they might be damned?
And does all this occur too in accordance with a plan entertained from eternity?
Then it follows that from all eternity He decreed for wise purposes to permit the entrance of moral evil into His system to permit men to use the powers He gave them in opposition to His authority; then, it follows that some were before of old (i.e. from eternity),
ordained to condemnation (Jude 4). Finally, it follows that the world, in all its physical and moral details, is just as God designed it to be.
Objection 1. "But does not this make God the author of sin?"
Let us get a definite idea of this phrase. What do you mean by the author of sin?
Sin is the transgression of the law, and the author of sin is one who is the perpetrator of such transgression. God, in this sense, cannot be the author of sin; nor can the Calvinistic doctrine of Predestination be tortured into such a blasphemous testimony against Him.
"But does it not teach that evil entered into His system in accordance with His eternal purpose and that He decreed all the acts of transgression that wicked men are guilty of; does it not, therefore, make Him the approver of sin?"
This question is a pertinent one, and we will meet it with all fairness. Predestination does assert that all the wicked acts of wicked men were foreordained before the beginning of time;
but yet
it as unequivocally asserts that God does not approve of them;
since it teaches that He before of old ordained them to condemnation because of those very sins.
"But how can God foreordain that of which He does not approve?"
I will answer your question by propounding another: How can God, when He possesses infinite power, permit that of which He does not approve?
When you have answered my question, you will have furnished an answer to your own.
Now that moral evil does exist—that wicked men do sin against God, are facts that are indisputable. This happens either by God’s permission or against His consent.
Now let my Arminian interrogator take either supposition that he pleases.
If he says that wicked men sinning against God happen against God’s consent—in spite of God’s will, then he robs Him of His omnipotence;
if he says that wicked men sinning against God happen by God’s permission, then he too is imperatively called upon to defend his system from the odious consequences which he ascribes to mine.
The only difference between us is that
he (the Arminian) says God permits sin,
(& wicked men sinning against God)
and we (the Calvinists) say that He decreed from eternity to permit it (wicked men sinning against God).
"Him, being delivered by the determinate counsel and foreknowledge of God, ye have taken, and by wicked hands have crucified and slain:"
Acts 2:23.
Check this out AustinC: I want you to find out for me, how do wicked men sinning, "by the determinate counsel and foreknowledge of God", not cause God to be the author of sin? 
