How can one "buy" oil and "buy" gold, garments, and eye salve if these things can only attained by grace? From the account of the 10 virgins in Matthew 25, and from the exhortation to the Laodicean Church in Revelation 3:14-22,  What is meant by the instruction to "buy" oil, gold, garments and eye salve? It is my understanding that these all represent items that cannot be purchased by man, but instead were already purchased by Christ's death on the cross and given to man upon acceptance of His sacrifice?

Matthew 25:1-9 (NASB):


  “Then the kingdom of heaven will be comparable to ten virgins, who took their lamps and went out to meet the bridegroom. Five of them were foolish, and five were prudent. 3 For when the foolish took their lamps, they took no oil with them, 4 but the prudent took oil in flasks along with their lamps. Now while the bridegroom was delaying, they all got drowsy and began to sleep. 6 But at midnight there was a shout, ‘Behold, the bridegroom! Come out to meet him.’ Then all those virgins rose and trimmed their lamps. 8 The foolish said to the prudent, ‘Give us some of your oil, for our lamps are going out.’ But the prudent answered, ‘No, there will not be enough for us and you too; go instead to the dealers and buy some for yourselves.’”


Revelation 3:14-22:


  “To the angel of the church in Laodicea write: The Amen, the faithful and true Witness, the Beginning of the creation of God, says this:‘I know your deeds, that you are neither cold nor hot; I wish that you were cold or hot. ‘So because you are lukewarm, and neither hot nor cold, I will spit you out of My mouth. ‘Because you say, “I am rich, and have become wealthy, and have need of nothing,” and you do not know that you are wretched and miserable and poor and blind and naked, I advise you to buy from Me gold refined by fire so that you may become rich, and white garments so that you may clothe yourself, and that the shame of your nakedness will not be revealed; and eye salve to anoint your eyes so that you may see. ‘Those whom I love, I reprove and discipline; therefore be zealous and repent. ‘Behold, I stand at the door and knock; if anyone hears My voice and opens the door, I will come in to him and will dine with him, and he with Me. ‘He who overcomes, I will grant to him to sit down with Me on My throne, as I also overcame and sat down with My Father on His throne. ‘He who has an ear, let him hear what the Spirit says to the churches.’”
They are only available by grace, which is why Jesus asked us to purchase it from Him. The fact that it is free grace does not mean it does not require cooperation from us. If we take the parable of the man who sold all to purchase a field where he believed the treasure was, likewise we should do similarly spiritually - to forsaken our attachment to the things of this world to purchase the things we most need from God. 

There is an exchange, it is our heart, our body, our soul. We are to surrender this to Christ. By purchasing the oil, the gold, the robe, the eye salve, we are building on our Christian experience with essentials not from us, going from faith to faith.