"Know that the Lord, he is God!
It is he who made us, and we are his;
we are his people, and the sheep of his pasture."
This verse is primarily dealing with God's protection, care and provision of the nation of Israel. God rescued the Jews from slavery in Egypt and he cared and provided for them as well as protecting them from their enemies in many and numerous ways as he brought them to the promised land and even after they settled in it. Even when they they forgot God and turned to idol worship which they did on many occasions God continued to love them. Repeatedly his sheep, Israel, grumbled, complained and rebelled against him despite the exalted position they enjoyed as his chosen people and the great care God had shown towards them. Despite this he continued to be the Shepherd of his sheep pictured here in this verse.
Jesus himself ultimately fulfilled and broadened the scope of God's Shepherd care to include both Jews and Gentiles. He did so by laying down his life.
"I am the good Shepherd. I know my own and my own know me, just as the Father knows me and I know the Father; and I lay down my life for the sheep. And I have other sheep that are not of this fold. I must bring them also, and they will listen to my voice. So there will be one flock, one Shepherd." (John 10:14-16)
I believe the following can be gleamed from Psalm 100:3 and from John 10:14-16 as it throws light upon this verse from the Psalm:
1) There is one God. There are not many God's as Roman and Greek mythology teach or as religions such as Buddhism and Hinduism teach. Instead there is only one God. This God we can know since he revealed who he is in the bible.
2) God created all things including all peoples of different beliefs, nationalities, cultures and tongues.
3) From all the people's of the world God has chosen a particular people which was the nation of Israel in the Old Testament but which through Jesus has been extended to include all people's of different ethnicites and languages so that it is no longer restricted to Jews. This is called the Church in the New Testament.
4) This people are defined as "his sheep." This indicates that they have one greater than themselves watching over them, who knows their needs, and who cares and provides for them as well as protects them from enemies who would seek to harm them.
5) Jesus said, "I know my own and my own know me." The Shepherd has intimate knowledge of those who belong to him. he distinguishes them from all those who surround them since he has known who they were since before the foundation of the world. Therefore when Jesus dies on the cross he knows those who he is dying for.
6) But the sheep also know the Shepherd. In John 10:4 it says,
"When he has brought out all his own, he goes before them, and the sheep follow him, for they know his voice."
The sheep know and follow the voice of Jesus. His voice carries such authority and power that when his sheep hear it they always follow since it awakens, causes life, faith and obedience. Jesus' voice is divine in its impact so that it has the ability to create and do what is spoken such as when "by the word of the LORD the heavens were made, and by the breath of his mouth all their host." (Psalm 33:6) And by his word Jesus caused the dead to rise from the grave such as in the case of Lazarus when he said, "Lazarus, come out" and Lazarus came out.
7) In Jesus God the Shepherd cares and provides for as well as protects his sheep by laying down his life for them on a cross to save them from the coming danger of judgment and wrath and to reconcile them to God.
8) In Psalm 100:3 it says,
"Know the Lord, he is God."
We are to experience the truth that this is who God is for us in Jesus. As he cared for, protected, provided for and guided Israel in the Old Testament, and his Church in the New Testament he will do so for the Christian today. And we are to be assured that we have a great Shepherd who cares with such love for the welfare and well-being of his sheep that he was even willing to give of his own life for them.