John 4:10 Jesus answered and said to her, “If you knew the gift of God, and who it is who says to you, ‘Give Me a drink,’ you would have asked Him, and He would have given you living water.”

Calvin on knowing Christ as the gift of God:

   These two clauses, If thou knewest the gift of God, and, who it is that talketh with thee, I read separately, viewing the latter as an interpretation of the former. For it was a wonderful kindness of God to have Christ present, who brought with him eternal life. The meaning will be more plain if, instead of and, we put namely, or some other word of that kind, thus: If thou knewest the gift of God, namely, who it is that talketh with thee. By these words we are taught that then only do we know what Christ is, when we understand what the Father hath given to us in him, and what benefits he brings to us. Now that knowledge begins with a conviction of our poverty; for, before any one desires a remedy, he must be previously affected with the view of his distresses. Thus the Lord invites not those who have drunk enough, but the thirsty, not those who are satiated, but the hungry, to eat and drink. And why would Christ be sent with the fullness of the Spirit, if we were not empty?
   Again, as he has made great progress, who, feeling his deficiency, already acknowledges how much he needs the aid of another; so it would not be enough for him to groan under his distresses, if he had not also hope of aid ready and prepared. In this way we might do no more than waste ourselves with grief, or at least we might, like the Papists, run about in every direction, and oppress ourselves with useless and unprofitable weariness. But when Christ appears, we no longer wander in vain, seeking a remedy where none can be obtained, but we go straight to him. The only true and profitable knowledge of the grace of God is, when we know that it is exhibited to us in Christ, and that it is held out to us by his hand. In like manner does Christ remind us how efficacious is a knowledge of his blessings, since it excites us to seek them and kindles our hearts. If thou knewest, says he, thou wouldst have asked. The design of these words is not difficult to be perceived; for he intended to whet the desire of this woman, that she might not despise and reject the life which was offered to her.

—John Calvin, Calvin’s Commentaries Volume XVII, Commentary on the Gospel according to John, Volume I (Baker Books, 2009), 148–149.