Romans 1:4

Romans 1:4 And declared to be the Son of God with power, according to the spirit of holiness, by the resurrection from the dead:

Since this verse begins with the word "and", we must understand what verse three ended with so that we will be able to fully understand verse four. 

Verse three we are introduced to the Gospel of God which was concerning His Son, Jesus Christ.  The gospel of God had to do with the presentation of Jesus Christ as the seed of David which had long before been prophesied.  We then come to verse four where we are told that Christ was also declared to be the Son of God with power.  The power He has was shown by the resurrection from the dead. 

The phrase, "according to the spirit of holiness" is something we need to take a close look at as well.  How are we able to  know that Christ was the seed of David, that He was declared to be the Son of God, and that he was to die and then be resurrected?  This answer can be found by understanding verse two.  We are able to read the scriptures wherein we will find the information that is laid before us.  Who wrote the scriptures?  2 Peter 1:21, "For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost."  Men wrote down the word of God as the Holy Spirit told them what to write.  The scripture is not the imagination of man, nor is it something people wrote down because of their personal feelings toward God.  The words on the page were inspired by God Himself and they were communicated to men who then wrote them down.  This is the whole idea behind the Doctrine of Inspiration and the Doctrine of Preservation.  God told us in His word that He spoke the words and promised to keep them forever.  It is within this holy script we find the truth about the coming, the death, and the resurrection of Jesus Christ. This is what the Gospel of God contains, this is what Isreal was given for centuries, and this is what they were to preach. 

However, we know that they failed at doing so, since they decided to crucify Him and chose rather to have Barabbas released unto them.