1. Christ will suddenly come to us. (Mal 3:1)
    2 Pt 3:9-10, Mt 24:42-43, 1 Thess 5:2-3

In the Old Testament, God said that Christ would suddenly come to the temple. (Mal 3:1)

Mal 3:1 Behold, I will send my messenger, and he shall prepare the way before me: and the Lord, whom ye seek, shall suddenly come to his temple, even the messenger of the covenant, whom ye delight in: behold, he shall come, saith the Lord of hosts.

Christ will return as a thief when we do not know. Therefore, we must be awake. (2 Peter 3:9-10, Matthew 24:42-43, 1 Thessalonians 5:2-3)

2 Peter 3:9 The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance.
10 But the day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up.

Matthew 24:42 Watch therefore: for ye know not what hour your Lord doth come.
43 But know this, that if the goodman of the house had known in what watch the thief would come, he would have watched, and would not have suffered his house to be broken up.

1 Thessalonians 5:2 For yourselves know perfectly that the day of the Lord so cometh as a thief in the night.
3 For when they shall say, Peace and safety; then sudden destruction cometh upon them, as travail upon a woman with child; and they shall not escape.