Isaiah 41:4 (ESV Strong's)
Who has performed and done this,
calling the generations from the beginning?
I, the LORD, the first,
and with the last; I am he.
The generations of the Lord are His people we have come to know as Israel, who trace their ancestry through their fathers. This gives them the context of who they are in life. They serve the one God Almighty by bringing His word into the world.
The sons of God have one Father from above. We are the single generation of those who are in the kingdom of heaven. This is the context of who we are in the life of the Lord. We serve the one God by joining our lives with His word and worship in the Spirit.
The last work of the Lord in creation is man made in the image of God. We first begin in the flesh of man, then enter the body of Christ, and are made in the exact image of God in creation who is Christ Jesus.