Answer: God, by an eternal and immutable decree, out of his mere love, for the praise of his glorious grace, to be manifested in due time, has elected some angels to glory₁; and in Christ has chosen some men to eternal life, and the means thereof₂: and also, according to his sovereign power, and the unsearchable counsel of his own will (whereby he extends or withholds favor as he pleases), has passed by and foreordained the rest to dishonor and wrath, to be for their sin inflicted, to the praise of the glory of his justice.₃

1. 1 Timothy 5:21
2. Ephesians 1:4-6; 2 Thessalonians 2:13-14
3. Romans 9:17-18; Romans 9:21-22; Matthew 11:25-26; 2 Timothy 2:20; Jude 1:4; 1 Peter 2:8

For further study see:

1. Elder Gregory Moeck of First Orthodox Presbyterian, San Francisco explains WLC 13
   
2. Elder Gregory Moeck of First Orthodox Presbyterian, San Francisco explains WLC 13 (part 2)