Luke 1:50 :
His mercy is for generations of generations on those who fear him.
Mercy can be defined as not getting the punishment that we deserve. Mary was aware that she, as all humanity, deserved punishment. She was also made aware by the Holy Spirit that God has so much mercy that he has enough for generation after generation of people that revere Him.
Mary only knew “the God of the Old Testament” because the New Testament was yet to be written. Mary’s God had lots of mercy as we read here. Some have believed that that God in the Old Testament was different than in the New, but that is not the case. The Bible tells us that God never changes.
We were the ones who were changed when God sent His Son to die for our sins. God showed us mercy by allowing this to happen and because we were cleaned by Jesus death, the God of the Old Testament was able to have a new relationship with the people of the New Testament. If it were not for Jesus Christ, the one and only God would have to deal harshly with us. In fact, those who don’t believe in Jesus as the only way to God, will someday face that harsh reality again when He returns.
Some people wonder why Jesus is taking so long in returning to earth as He promised. I suggest that one good reason that He hasn’t returned yet is because He is demonstrating the enormity of his mercy to generation after generation after generation so that we understand the lengths that God goes to help us. God didn’t have to wait any amount of time, but God loves us and He wants many people to come to Him. Some of them may have even been born today. We should be thankful to God for His mercy as he waits to send Jesus back to get us, but remain eager and ready to see Him return.