Understanding the Parable of the Sheep and the Goats lies in their surprised responses. Both the sheep and the goats respond, "When did we see you in need and help you?" (verses 37-39, 44). This parable contains two lessons.
The first lesson is that neither the sheep nor the goats are surprised at the place Christ assigns them. A careful reading of the parable shows that clearly. They do not respond to the place that Christ assigns them, but they express surprise at the reasons He gives for His judgment. A vital question to Christians is, on what does He base his judgment? The basis of His judgment is how they treated Christ! Of course, their treatment of Christ manifests itself in how they treated those in whom Christ lived, those who had His Spirit.
The second lesson is no less important than the first. Jesus, our Judge, eliminates the possibility of hypocrisy obscuring His judgment of the sheep and the goats. If the goats had thought that treating their brothers in the faith would have gotten them into the Kingdom, they would have done it. What is the lesson? Jesus is interested in love from the heart, not a false love.
The true love of God is seen in the sheep. As the sheep respond to their brother's need, they are united in their distress and at the same time unwittingly, unconsciously, without hypocrisy, align themselves with Christ. Apparently, they are not even aware of what they were doing. This is a kind of love that cannot be faked or put on. "By this all will know that you are My disciples, if you have love for one another" (John 13:35).
The reaction of the goats is quite different. They have little sympathy for God's way and remain indifferent, Laodicean, to their brethren. In so doing, they reject their Messiah, their King, since He lived in the people whom they would not serve. The goats are condemned because of their sins of omission.
Because they had developed their relationship with Christ through prayer, Bible study, fasting, and obedience, the sheep have love through a regular infusion of the Spirit of God. "[T]he love of God has been poured out in our hearts by the Holy Spirit who was given to us" (Romans 5:5). A godly life always comes down to the basic things. The sheep are simply unconsciously and unaffectedly good, kind, sympathetic, and concerned, attributes of character that cannot be feigned.