As much as we tend to judge past and present Christians on their behavior and use our understanding of those behaviors to declare or reject a personal trust in God, we would do well if we stepped back from our judgments and looked at the facts.
Yes, Jacob doubted. Yes, Leah and Rachel connived and manipulated. Yes, the boys battled jealousy well into their 50's at least. Yes, the descendants of these children, loved by God, didn't get it right and didn't always follow God as well as you or I may have if we were in their sandals. Despite all their efforts to make God look bad, the fact remains:
God never changed. God never broke his promises to those who doubted. His promises were never contingent upon their belief in his ability to keep them. His promises were made because he could keep them.
God keeps his promises. It does not depend on us trusting in his promises for them to be kept. God remains true to himself and his word for his sake, not ours. He is not waiting for us to trust his promises in order for him to fulfill them.
A promise from God is the greatest guarantee one could ever get from anyone or anything. A promise from God far outweighs any notarized piece of paper or any contract a man or woman can sign.
Bible Gateway states there are 5467 promises of God. Won't you take a look and see how many promises speak to you. Enjoy the journey.