2 For when the Jews had said, “Say we not well that you are a Samaritan, and hast a devil?” of these two charges cast at Him, He denied the one, but not the other. For He answered and said, “I have not a devil.” He did not say, I am not a Samaritan; and yet the two charges had been made. Although He returned not cursing with cursing, although He met not slander with slander, yet was it proper for Him to deny the one charge and not to deny the other. And not without a purpose, brethren.
For Samaritan means keeper. He knew that He was our keeper. For “He that keeps Israel neither slumbers nor sleeps;” and, “Except the Lord keep the city, they wake in vain who keep it.” He then is our Keeper who is our Creator. For did it belong to Him to redeem us, and would it not be His to preserve us? Finally, that you may know more fully the hidden reason why He ought not to have denied that He was a Samaritan, call to mind that well-known parable, where a certain man went down from Jerusalem to Jericho, and fell among thieves, who wounded him severely, and left him half dead on the road.
A priest came along and took no notice of him. A Levite came up, and he also passed on his way. A certain Samaritan came up— He who is our Keeper. He went up to the wounded man. He exercised mercy, and did a neighbor's part to one whom He did not account an alien. To this, then, He only replied that He had not a devil, but not that He was not a Samaritan.
Source: Tractates on the Gospel of John (New Advent)