It means that there is no hope or plan of salvation and reconciliation with God outside of the Cross and the Resurrection of Jesus Christ.
Christ is the Last Adam and so is a new prototype, a new seed for all Mankind, although it only manifests inside of those who believe in Him.
We cannot preach salvation be repentance, good works, alms, indulgencies, tithing, evangelism or anything.
Each human must be baptized into Christ death and by default Resurrection. Nothing else has any saving power.
3 Or do you not know that as many of us as were baptized into Christ Jesus were baptized into His death? 4 Therefore we were buried with Him through baptism into death, that just as Christ was raised from the dead by the glory of the Father, even so we also should walk in newness of life.
” (Romans 6:3–4, NKJV)
20 I have been crucified with Christ; it is no longer I who live, but Christ lives in me; and the life which I now live in the flesh I live by faith in the Son of God, who loved me and gave Himself for me. ” (Galatians 2:20, NKJV)
18 For the message of the cross is foolishness to those who are perishing, but to us who are being saved it is the power of God. 19 For it is written:
“I will destroy the wisdom of the wise,
And bring to nothing the understanding of the prudent.”
20 Where is the wise? Where is the scribe? Where is the disputer of this age? Has not God made foolish the wisdom of this world? 21 For since, in the wisdom of God, the world through wisdom did not know God, it pleased God through the foolishness of the message preached to save those who believe. 22 For Jews request a sign, and Greeks seek after wisdom; 23 but we preach Christ crucified, to the Jews a stumbling block and to the Greeks foolishness, 24 but to those who are called, both Jews and Greeks, Christ the power of God and the wisdom of God. 25 Because the foolishness of God is wiser than men, and the weakness of God is stronger than men.
” (1 Corinthians 1:18–25, NKJV)
2 And I, brethren, when I came to you, did not come with excellence of speech or of wisdom declaring to you the testimony of God. 2 For I determined not to know anything among you except Jesus Christ and Him crucified. 3 I was with you in weakness, in fear, and in much trembling. 4 And my speech and my preaching were not with persuasive words of human wisdom, but in demonstration of the Spirit and of power, 5 that your faith should not be in the wisdom of men but in the power of God.
” (1 Corinthians 2:1–5, NKJV)