We find Judas at this time in perfect union with Satan to do the Devil's bidding to betray Christ, something that is not very pleasant to consider. How can people turn their backs on the truth, on God Himself?
We can discern a logical progression because as union with one strengthens, union with the other weakens. In Judas' case, the union with God weakened. Why? He was entertaining thoughts that were in opposition to the spirit, to the mind, to the words of God. He allowed these ideas to grow through circumstances that arose in his life, and they kept getting stronger. His union with Satan, who was undoubtedly pumping these ideas into him or putting perverse twists on what he heard so that he began to feel alienated and separated from Christ, became stronger. At the same time, his union with God decayed until he betrayed Jesus.
This can happen to us, so we must fight against it. Married people ought to be able to understand how this works, as it is what happens when a divorce occurs. Usually, a married couple begin their union feeling as though they will never separate; they feel an intense bond with one another. But because their union is not worked at, gradually one or the other begins to be attracted to union with another. Everybody has to be on guard against this.
When the Bible speaks about guarding, keeping, preserving, and enduring, it is referring to this possibility. We must work to endure and preserve our union with God - and keep working at it to make it strong. How do we make a strong relationship? In the same way a couple works at it before they are married. In their dating and courtship, they do everything they can to please the other so that a union occurs. It is simple to grasp in principle but sometimes hard to do.