The only reason why you fight the truth is because you are afraid of the healing it brings – you love your sickness and helplessness. It's either that (being scared of the hurt that truth does to your lies and comfort zones) or you are empty: filled with spirits and reasons to be an opposition to truth.
For GOD, it was about bringing the Messiah at the right time and being patience for that time to come.
For Rebekah, it was not different. To walk against the traffic of (wrong) tradition(s) and obey the Voice of GOD; to be drenched in obedience enough to be used as a vessel – regardless of adverse effect.