Doesn't preaching God's soverignty require one to acknowledge the truth of every inspired Scripture, especially those which give us insight into His decisionmaking? In the case of
1 Corinthians 1:21, God's peasure is stated to be in saving those who believe. And the grammar makes it clear that "those who believe" are the direct objects of His action "to save". The grammar prevents a "reverse" understanding (i.e., that "to believe" is the result of "being saved").
[
1Co 1:18 KJV] 18 For the
preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God.
[1Co 1:21 KJV] 21
For after that in the wisdom of God the world by wisdom knew not God, it pleased God by the foolishness of preaching to save them that believe.
1 Co 1:21 verse should be understood in its proper context rather than taken in isolation.
According to the 1 Co 1:18 (above), the unsaved—those who are perishing—see the message of the cross as foolishness, while only those who are saved recognize it as the power of God. If the unsaved are bound by this perception of foolishness, how then can they believe before salvation?
In verse 1:21, the verse you quoted, Paul also says that “the world through wisdom did not know God.” If God cannot be known through human wisdom, then a person cannot come to true belief in Him by natural ability. Something must first occur in a person that comes from outside of themselves because the spiritually dead have no such ability. In vs 1:21, the "to save", is in the Aorist tense, and according to my limited understand of Greek, being Aorist, actually means a completed action not a future action relative to believing. IOW, the while the preaching was for them to believe, the saving already completed (Aorist).
[1Co 1:30 KJV] 30
But of him are ye in Christ Jesus,
who of God is made unto us wisdom, and righteousness, and sanctification, and redemption:
Verse 1:30 reinforces this with the phrase, “of him are ye in Christ Jesus, who is made unto us...,” showing that we are placed in Christ Jesus entirely by God’s work, not the result of our belief. And because we are in Christ, wisdom, righteousness, sanctification, and redemption are given freely to us as gifts from God, not as things received through our belief.