The LORD said to her, "Two nations are in your womb, and two peoples from within you will be separated; one people will be stronger than the other, and the older will serve the younger." When the time came for her to give birth, there were twin boys in her womb. (Genesis 25:23, 24)
Rebecca had questions for the Lord when she got pregnant. The Bible says,
The babies jostled each other within her, and she said, "Why is this happening to me?" So she went to inquire of the LORD. (Genesis 25:22)
What we read above was God's reply to her and in the fullness of time, what the Lord said came into being.
Rebecca remembered the Lord's words, "the older will serve the younger." Later on as her sons grew up she planned on her own to bring into effect the Lord's plan, but that was a disaster. She made Jacob, the younger son, deceive his almost blind father to receive the blessings due his elder brother Esau. Jacob had to go away from home and returned only after 20 years.
When God gives us a promise, he will guide us by his Holy Spirit to accomplish what he has planned or decided. Making our own plans to fulfil God's promise may eventually result in chaos and sorrow for the persons involved.
God is able to fulfil his plans for our lives. All we need to do is to be receptive to his voice and guidance and walk and act on his counsel. Then his plans will be fulfilled at the right time. Praise the Lord.