The passage
      v18. Paul begins by exposing the contrast between the message of the gospel and human wisdom. Those who follow the wisdom of this world find the gospel foolishness, but then they are perishing, while believers are "being saved".
      v19. Isaiah 29:14 originally served to warn Israel against thinking they could outwit God. Paul uses the warning as a prophetic reminder to his readers.
      v20. The rhetorical questions used in this verse follow on from v19. Christ's work on the cross has already, in a sense, destroyed the wisdom of the wise. Where do they stand now? The grace of God, exhibited in the cross, has bypassed worldly wisdom, a wisdom that claims a way into the presence of God.
      v21. It is plain enough that worldly wisdom is limited. It has not succeeded in providing a way to God, let alone securing a permanent relationship with him, or perfecting the human race. The pagan has ended up playing with idolatry, the Jew with legalism.... In the midst of this confusion, God has chosen to gather a people to himself and perfect them through the preaching of a message which rests on the crucifixion of Christ. By believing this message, a person can appropriate the benefits of Christ's work on the cross, namely salvation.
      v22. Jews demand messianic signs to confirm the truth, but the only sign given is the sign of Jonah - the preaching of the gospel. Gentiles demand worldly wisdom to confirm the truth, but the only wisdom given is the foolishness of the cross of Christ.
      v23. God's revelation to humanity in Christ is a contradiction - a messiah under the curse of God (cursed is everyone who hangs on a tree, Deut.21:23). The Jews believed that the coming messiah would be a glorified figure of power and might. Therefore, "Christ crucified" is certainly a "stumbling block to Jews", and as for Gentiles, it is "foolishness".
      v24. The called-out ones, that is, invited seekers, hear the foolishness of the gospel and find in it the power and wisdom of God. For the seeker, the perspective is different. They find the gospel able to move them into a right relationship with God. Thus, the gospel is the power of God unto salvation. The seeker also finds that the gospel is a message of majestic wisdom. The gospel is indeed wisdom to those who are being saved.
      v25. If the cross is foolishness, then it is God's foolishness, and God's foolishness is always wiser than human wisdom.

Sugar coating the gospel
      Some years ago a youth fellowship committee approached their senior pastor for his guidance on the fall in membership that they were experiencing at the time. They were having difficulty getting the local young people involved in their youth programme. They were trying everything, but the numbers were still low and they didn't seem to be getting anywhere. The pastor's response was right to the point; "If Christ can't attract them, then nothing can."
      The pastor had gone to the heart of the matter. Believers are really not in the business of making Christianity attractive and acceptable - "environmentally friendly." We are simply in the business of displaying Christ and him crucified. If that doesn't grab the lost, then nothing will.
      Yet, it seems that we are often unable to leave it at that. The business of making Christ known often becomes a subtle marketing exercise, a sociological experiment, an issue of group dynamics. And as for living the Christian life, progressing in the Christ life, the cross of Christ is left far behind as we explore the depths of piety, religiosity and spiritual ecstasy.
      The business of evangelism is simply a matter of communication - "we preach Christ crucified." Evangelism that rests on institutional management, marketing, or group dynamics has sold out to the "wisdom of the world" and serves only to empty the cross of its power. All we need to do is communicate the message as a banner. We are not to manipulate a response, but rather provide the key to salvation for those who are seeking it. For those who "seek" and "knock", the gospel is wisdom indeed.

v19
      gegraptai (grafw) "it is written" - write. "It stands written." Quote is from the LXX, Isaiah 29:14.
      thn sofian (a) "the wisdom" - The wisdom of the wise is a way of thinking, a worldly reasoning.
      aqethsw (aqetew) "I will frustrate" - set aside, disregard, repudiate. The LXX has "I will hide"

v20
      tou suzhththV "the philosopher" - disputant, debater.
      tou aiwnoV (wn onoV) "of this age" - Used here of the age stretching out to the dawning of the new age, eternity. The word has a similar meaning to "this world" and the "world to come."
      emwranen (mwrainw) aor. "made foolish" - regard something as a nonsense, as dumb. "God revealed the world's wisdom as folly", possibly made it a folly, but "revealed" is closer to the meaning of the text.

v21
      en "in" - Either i] local, ie. sphere of influence, place. God's wisdom is seen in his creative works, but the world did not recognize it. ii] Instrumental, "by" referring to God's plan of salvation. "For since, by God's wise plan, the world, exercising its own wisdom, did no know God, God chose to save those who had not wisdom, but faith, not by their own wisdom, but by the folly of the Christian preaching", Barrett.
      th/ sofia/ (a) "wisdom" - Here it is a good wisdom, God's wisdom. If option [ii] above is chosen, the wisdom is God's plan of salvation. God's wisdom focuses on the cross and is therefore, regarded as foolishness by the standards of human reasoning.
      egnw (ginwskw) aor. "know" - Although God's presence is clearly observable in creation, flawed human reasoning (a wisdom affected by the fall) devalues the evidence and therefore does not produce a knowledge of God. The knowledge of God comes by faith/folly, not by human reasoning (wisdom). It is possible Paul is arguing against those who contend that they can know God through wisdom.
      eudokhsen (eudokew) aor. "was pleased" - "please", but also an act of the will like "choose" , as here "chose."
      tou khrugmatoV (a atoV) "of what was preached" - the proclamation, Christian preaching. Paul is using the word of gospel communication, even the content of gospel communication, namely the cross, but not of preaching in church.

v22
      epeidh conj. " -" - since, because. A repetition of the beginning of v21, but it's causal strength must be limited otherwise v23 doesn't quite work.
      aitousin (aitew) pres. "demand" - ask. They are without faith and therefore ask for a visible evidence.
      EllhneV "Greeks" - here the same as Gentiles, or maybe particularly those who seek to know God through worldly wisdom.
      zhtousin (zhtew) pres. "look for" - seek

v23
      khrussomen ( khrussw) pres. "preach" - proclaim as heralds. Modern meaning is "communicate."
      estaurwmenon (staurow) perf, pas. part. "crucified" - having been crucified. The participle is adjectival, modifying Christ, "who has been crucified." The content of the communication is "Christ crucified." Everyone brings their own bias to the exposition of this phrase. For example, the atonement is a popular focus. Yet, Paul is into comparing a worldly wisdom with a divine wisdom. The worldly person seeks to know the divine through reason (wisdom) - a reaching up to God. Yet, the gospel proclaims that God has graciously reached down to us through the cross such that knowing God is through faith rather than wisdom. To the child of human reasoning, such is a foolishness. So "Christ crucified" is probably best expounded in the terms of God's grace.
      skandalon (on) "stumbling block" - something that trips someone up, a cause of stumbling.

v24
      autoiV de toiV klhtoiV (kalew) "but to those whom God has called" - but to the called ones, those who are called. The call of God is always a difficult concept, given that Paul never fully teases it out. It may simply mean "invitation", but then it may mean "effectual call". God's call of a people to himself is often described in "effectual" terms, although of individuals it is often in terms of "invitation." Robertson and Plummer suggest that the phrase is parallel to v18, "us who are being saved" - "actual believers." So, we are probably dealing with "an appeal to personal experience" rather than an effectual call or invitation to salvation.
      Criston (oV) "Christ" - Most likely "Christ crucified" is implied here rather than the person of the messiah.
      dunamin (iV ewV) "power" - For those being saved the cross is not a scandal, a useless sign, but is rather the power of God unto salvation.
      sofian (a) "wisdom" - Here the wisdom of God may be something more than his wise plan, it may be his effectual plan.