Many by the gift of God here understand Christ, whom God gave to the world, 1 Thessalonians 3:16; and who is the greatest gift that God ever gave to the world; so as the latter words, who it is, &c., expound the former. Thou wouldst have asked of him, and he would have given thee, either a true knowledge of the doctrine or the grace tendered in the gospel; or the Holy Spirit, called water, because it washes and cleanses the soul; and living water, because it is always running and flowing.
Related Commentaries of John 4:10
John 4:10
10 Jesus answered and said unto her,If thou knewest the gift of God, and who it is that saith to thee, Give me to drink; thou wouldest have asked of him, and he would have given thee living water.