I found this quote by Calvin helpful as our church studies Romans 9 together. Calvin’s emphasis on union with Christ throughout his writings again pays dividends as he reminds us to look to Christ to know that you are loved by God…and will be so forever. If we have been united to Christ by faith then we have no need to look into the past and be puzzled if God chose us. Christ is our assurance so we look at him.
But if we have been chosen in [Christ], we shall not find assurance of our election in ourselves; and not even God the Father, if we conceive of him as severed from his Son. Christ, then, is the mirror wherein we must, and without self-deception may, contemplate our own election. For since it is into his body the Father has destined those to be engrafted whom he has will from eternity to be his own…we have sufficiently clear and firm testimony that we have been inscribed in the book of life if we are in communion with Christ. (Calvin, Institutes, 3.24.5)