John emphasizes the word "kingdom" (Greek is written emphatically to draw attention to certain words). The other two words, "tribulation" and "patience," are like parentheses on both sides of the word "kingdom." What this does is to cause the word "tribulation" to define the path to the kingdom! Think of tribulation in terms of trials and pressures that arise as a result of our faith in Jesus Christ, our journey toward God's Kingdom, and our faith that we will be a part of it. The way to the Kingdom of God is through trials. We will not just skate along because God has created work for us to accomplish in our lives so that we might be prepared for the Kingdom. If we are not prepared for it, we will not be there.
The way of preparation is for God to put us through trials, just as if we were going to school. We can think of trials in terms of lessons that need to be learned, character that needs to be built, attitudes that need to be adjusted. All of these put pressure on us. So tribulation—pressure or trials—is the path. "All who desire to live godly in Christ Jesus will suffer persecution" (II Timothy 3:12). We are going against the flow of the world, and God has designed it this way to prepare us for His Kingdom. Thus, there will always be pressure on us.
Pressure is the way to the Kingdom, and patience is the necessary element for making it. If we are impatient, we will not be there! Salvation is by grace through faith, and faith is needed when we do not have what we desire—the Kingdom of God. There is no need for faith if we do not have to wait! Patience is required while we are waiting. It is that simple.
The way to the Kingdom is through testing and trial, and the way to succeed in testing and trial is to put our faith to work by being patient! That is the path that will exercise our faith. God will see that it is there, and His creative efforts on our behalf will work. All of us must have patience. It is there, but it has to be activated. We have to trust that God really wants us in His Family, and if we want to be prepared for His Kingdom, we had better start using patience.