Well after all Jesus had not died yet. He preached the Kingdom of God to the masses, but He shared the plan of salvation with His inner circle of disciples, who then after His death, went out and spread/taught the gospel of God's grace.
The old testament had plenty of scriptures that taught of the grace of God long before Jesus was even born as a baby. So it all ties in together as one.
Do you believe Jesus is in heaven sitting on the right hand of God the Father at this time as well as the Holy Spirit dwelling within a christian's heart?