When the time had fully come the Father sent His Son among us as one of us. In this event we see the eternal will and purpose of God become actual among us. Yes, as we fix our eyes on this one man, we know what was the will of God at the beginning of all time, and even before time. We see opened to us the eternal purpose- God with us and we with God in union with the Father’s Son.
But surely we get to know God’s eternal will and purpose by studying bible texts that speak about His eternal decrees. God has decreed certain things before the foundation of the world. We simply look at the texts that speak about these eternal decrees and make logical deductions from them. I used to approach God’s eternal purpose this way. I ended up with a warped view of God. A God who fixes the eternal destiny of individuals before they are even born. A God who has to be difficult to trust. You can never really be sure if He has fixed your own destiny as one of the chosen ones.
Now I see that there is only one revelation of the eternal will and purpose of God. The revelation of God Himself in the man Jesus. So if we try to invent a doctrine of God’s eternal decrees apart from Jesus we will end up with an idol. And not a very attractive one! But with our eyes fixed on Jesus we are drawn into assured fellowship with our Father in the Spirit. We know for sure that Jesus is the Father’s chosen one and in union with him, by the Spirit, we share in His close relation with the Father.