Luke 10:25-37
25 And behold, a certain lawyer stood up and tested Him, saying, “Teacher, what shall I do to inherit eternal life?”
26 He said to him, “What is written in the law? What is your reading of it?”
27 So he answered and said, “ ‘You shall love the LORD your God with all your heart, with all your soul, with all your strength, and with all your mind,’ and ‘your neighbor as yourself.’”
28 And He said to him, “You have answered rightly; do this and you will live.”
29 But he, wanting to justify himself, said to Jesus, “And who is my neighbor?”
30 Then Jesus answered and said: “A certain man went down from Jerusalem to Jericho, and fell among thieves, who stripped him of his clothing, wounded him, and departed, leaving him half dead. 31 Now by chance a certain priest came down that road. And when he saw him, he passed by on the other side. 32 Likewise a Levite, when he arrived at the place, came and looked, and passed by on the other side. 33 But a certain Samaritan, as he journeyed, came where he was. And when he saw him, he had compassion. 34 So he went to him and bandaged his wounds, pouring on oil and wine; and he set him on his own animal, brought him to an inn, and took care of him. 35 On the next day, when he departed, he took out two denarii, gave them to the innkeeper, and said to him, ‘Take care of him; and whatever more you spend, when I come again, I will repay you.’ 36 So which of these three do you think was neighbor to him who fell among the thieves?”
37 And he said, “He who showed mercy on him.”
Then Jesus said to him, “Go and do likewise.”
While there might not be any way to reach the Father, except through the Son, (Jesus is the "gate.") Jesus did say he had "other sheep, not of this fold," and that a
hireling who does not own and love the sheep will allow the wolves to scatter the sheep. I would say that this means there are sheep who hear the voice of the good shepherd, who are not part of the same "fold" as the Christians, but hear the voice of the Good Shepherd, nonetheless, just like the Good Samaritan mentioned above (parable was given in reference to the question:
“Teacher, what shall I do to inherit eternal life?”)
John 10:7-16
7 Then Jesus said to them again, “Most assuredly, I say to you, I am the door of the sheep. 8 All who ever came before Me are thieves and robbers, but the sheep did not hear them. 9 I am the door. If anyone enters by Me, he will be saved, and will go in and out and find pasture. 10 The thief does not come except to steal, and to kill, and to destroy. I have come that they may have life, and that they may have it more abundantly.
11 “I am the good shepherd. The good shepherd gives His life for the sheep. 12 But a hireling, he who is not the shepherd, one who does not own the sheep, sees the wolf coming and leaves the sheep and flees; and the wolf catches the sheep and scatters them. 13 The hireling flees because he is a hireling and does not care about the sheep. 14 I am the good shepherd; and I know My sheep, and am known by My own. 15 As the Father knows Me, even so I know the Father; and I lay down My life for the sheep. 16 And other sheep I have which are not of this fold; them also I must bring, and they will hear My voice; and there will be one flock and one shepherd.