Read Matthew 22.
The parable about the wedding banquet, here in verses 1-14, is about Israel’s rejection of Jesus as Messiah. God the Father invited them to the wedding banquet and everything was ready (vv. 1-4) but Israel was too busy with their own stuff, even getting angry enough to persecute and kill some of God’s servants, the prophets (vv. 5-6).
God judged Israel (v. 7 is a veiled prophecy of the destruction of Jerusalem in A.D. 70) and turned his attention to inviting us, the Gentiles through the gospel message (vv. 8-14).
Notice, though, that all the “bad as well as the good” (v. 10) were gathered in, you still needed an outfit appropriate for a wedding (vv. 11-12). Jesus did not explain what this meant other than verse 14’s statement that, “…many are invited, but few are chosen.” That statement does not explain the image of the wedding clothes and how it relates to the parable.
As God’s revelation continued to unfold in the New Testament, we can see clearly that the wedding clothes Jesus referenced in verses 11-12 refer to the righteousness of Christ that God credits to us by grace. When you and I put our faith in Christ, God began to treat us as if we are as righteous as Jesus Christ is, even though we are not.
Jesus’s perfect life clothes you like a garment. His atonement on the cross was applied to you when you trusted in him, washing all your sins away. But the perfect life of Jesus Christ was also gifted to you, covering your imperfections and making you acceptable in the sight of God.
You and I have a long way to go before we will actually be righteous in the sight of God. God is working on us to make us righteous people but you still belong at the wedding feast because you are covered by the righteousness of Christ.
This is why you don’t need to worry about “losing your salvation.” You didn’t earn your salvation in the first place. It was given to you by God. You can’t lose the garment of Christ’s righteousness any more than you can lose the shirt on your back. If you’re someone who struggles with feelings of assurance in your faith, let this passage encourage you. Trust in the gracious gift of Christ, not your own performance.