God has a purpose for everything He does and though He certainly is not obligated to explain Himself to any of us, He does typically reveal His motives through Scripture.
When discussing Romans 8:29 Calvinist’s will typically argue that a personal intimacy is in view.
Calvinism teaches that God foreknows because He decreed that man would act a certain way, and thus man necessarily acts a certain way and God can be certain of that.
To declare God’s glory is to talk about His greatness. God is great, and He is more than worthy of all praise and glory.
There is nothing contradictory nor deficient in understanding the biblical portrait of man’s knowledge being uncertain while God’s is certain