Arcana Coelestia #2624
2624. 'In his old age' means when the days had been completed for the human to be cast off. This becomes clear from the meaning of 'old age' as the state when He was to cast off the human and to put on the Divine, dealt with in 2198. For Abraham was at that time a hundred years old, a number which means a full and complete state of union, as will be clear from the explanation of verse 5.
Arcana Coelestia #1864
1864. That 'on that day Jehovah made a covenant with Abram' means the joining together of the Lord's Interior Man and His Internal Man is clear from the meaning of 'a covenant' as a joining together, dealt with already in 665, 666, 1023, 1038. Here, because in the internal sense the Lord is the subject, it means an interior conjunction. For the Lord advanced more and more towards conjunction and union with Jehovah His Father, till at length He became one, that is, the Human Essence itself also became Jehovah, who was the Lord's Internal itself. These things were represented by 'the covenant which Jehovah made with Abram'. Anyone may see that Jehovah never makes a covenant with man, for such would be contrary to the Divine. What is man but something base and filthy, which of itself thinks and does nothing but evil? All the good that he does comes from Jehovah. From this it becomes clear that this covenant, like every other covenant made with Abram's descendants, was nothing else than a representative of the Divine and of the heavenly things of the kingdom of God. This particular covenant made with Abram was a representative of the joining together of the Lord's Human Essence and His Divine Essence, that is, Jehovah. That it was a representative of the joining together of the Lord's Interior Man and His Internal Man, that is, Jehovah, is clear from what has gone before - that the Lord joined and united Himself more and more through the conflicts brought about by temptations and through victories. What the Interior Man was has been stated already, namely that which was between the Internal and the External.