What shall we then say to these things? If God [be] for us, who [can be] against us?
Note 4 at Ro 8:31: Ro 8 came as the answer to the hopelessness of the flesh ever pleasing God that Paul declared in Ro 7. Ro 8 is full of victory through the indwelling presence and power of the Holy Spirit.
Paul had just spoken of the Holy Spirit making intercession for us (Ro 8:26-27), God working all things together for our good (Ro 8:28), and us being predestined to be conformed to the image of Jesus (Ro 8:29). Here he was drawing a conclusion from all these things. If God be for us (which is exactly what he had been saying), then no one can successfully be against us. This is an exclamation of victory for the Spirit-controlled life that Paul continued teaching through the end of this chapter.