who, though he was in the form of God, did not count equality with God a thing to be grasped, (ESV)
This section of Scripture is of great importance. Here we have the Apostle Paul speaking of the Incarnation, God becoming flesh, and what that means for us. If you look at every single cult that distorts the truth of God's Word you will find that every single one of them make a mistake when it comes to the nature of Jesus Christ.
The Jehovah's Witnesses declare that Jesus was a created being. He was not God, but rather a god. The idea of equality with the Father is not accepted by their theology. The Mormons also make a mistake in this area. They declare that Jesus was one of many spirit beings created by God. He was not equal with God. In fact, he was the spirit brother of Lucifer in their teaching.
It is very important that we understand the truth of what God declares about the nature of Jesus Christ. If our Savior is not fully God than his sacrifice on our behalf would be ineffective. Also, if Jesus is not fully God than Jesus' own claims to deity would make him out to be a liar, Consider Jesus' words in John 10:30: "I and the Father are one.”
"Paul affirms that Jesus eternally has been God. The usual Greek word for “was” or “being” is not used here. Instead, Paul chose another term that stresses the essence of a person’s nature—his continuous state or condition. Paul also could have chosen one of two Greek words for “form,” but he chose the one that specifically denotes the essential, unchanging character of something—what it is in and of itself. The fundamental doctrine of Christ’s deity has always encompassed these crucial characteristics."
- Dr. John MacArthur, Online Study Bible Notes
Jesus was and is fully God. He took on human flesh in order to provide salvation. Be aware of those who would deceive you into thinking that Christ is anything less than eternal God.