Because of the ingratitude and obduracy of its inhabitants who would not receive Him as their Redeemer, and who through impenitence were hastening to destruction.
When was the time of visitation?
The period in which God sent them one prophet after another who urged them to penance, and whom they persecuted, stoned, and killed. (Matt. 23:34) It was especially the time of Christ's ministry, when He so often announced His salutary doctrine in the temple of Jersualem, confirmed it by miracles, proving Himself to be the Messiah, the Saviour of the world, but was despised and rejected by this hardened and impenitent city.
Who are prefigured by this hardened and impenitent city?
The hard-hearted, unrepenting sinners who will not recognize the time of God's visitation, in which He urges them by the mouth of His preachers, confessors, and superiors, and by inward inspiration to reform their lives and seek the salvation of their soul, but who give no ear to these admonitions, and defer conversion to the end of their lives. Their end will be like to that of this impious city; then the enemy, that is, the evil spirit, will surround their soul, tempt, terrify, and drag it into the abyss of ruin. Oh, how foolish it is to squander so lightly, the time of grace, the days of salvation! Oh, how would the damned do penance, could they but return to earth! Oh, how industriously would they employ the time to save their soul! Use, then, my dear Christian, the time of grace which God designs for you, and which, when it is run out or carelessly thrown away, will not be lengthened for a moment.
Will God conceal from the wicked that which serves for their salvation?
No; but while they are running after the pleasures of this life, as St. Gregory says, they see not the misfortunes treading in their footsteps, and as consideration of the future makes them uncomfortable in the midst of their worldly pleasures, they remove the terrible thought far from them, and thus run with eyes blindfolded in the midst of their pleasure into eternal flames. Not God, but they themselves hide the knowledge of all that is for their peace, and thus they perish.