When reformed theologians speak about the first cause and secondary causes, they do not mean sequences in time. They refer to two ORDERS of causality:
1. Divine (first cause);
2. Creaturely (second or contingent causes).
The reason why the first cause—logically prior, but of a different order than secondary causes—can concur with secondary causes is BECAUSE they are of a different order.
They CAN concur because they do not contradict each other, being of divine and human orders.
God is eternally present, before all things at once, and so he sees past, present, and future all at once. He does not cause something prior in time, but causes something in a way beyond our capacity to know.
Hence, our contingent choices can concur with God’s prior agency. If God in a way that transcends understanding can see all acts at once, he foreknows all things. That foreknowledge, in this sense predestination, means that God timelessly enacts his will.
His causation in such a way cannot be confused for ours! We think in sequence. We are contingent. We are ignorant of much. God is not. So our order of possible free choice exists in a different order of being—we can have genuinely free, contingent choice, without contradicting God’s freedom since our wills concur along different planes of being.