"He chose us in Him [Christ] before the foundation of the world that we should be holy and without blame before Him in love" (Ephesians 1:4). The doctrine of election, or being chosen by God, is all about Christ. Jesus is the Elect of God. He is the one chosen before creation to save God's people.
God chose us in Christ. How then are we in Christ? Only when a person hears the gospel of Christ and believes on him can it be said that he is in Christ (Romans 16:7). We are saved in Christ alone, by faith alone. Having believed on our Lord Jesus Christ, we are baptized by the Holy Spirit into the body of Christ (1 Corinthians 12:13). That's what it means to be in Christ.
God chose us in Christ to be the church, the body of Christ (1 Corinthians 12:27). In the Old Testament God's chosen people were known as the nation of Israel. In the New Testament, God's people are known as the church, which is both Jews and Gentiles who know Jesus Christ as Lord. Again, we see that God has chosen his people in Christ.
God chose us in Christ to be "holy and and without blame before Him in love" (Ephesians 1:4). We are blameless, because the blood of Jesus Christ cleanses us from all sin (1 John 1:7). We are holy because we have received the righteousness of God in Christ (Romans 3:24-26; 4:5). This should never be thought of as self-righteousness. It is the imputed righteousness of Christ, which we receive by grace through faith.