Ans. In order to rightly apprehend this statement, we must go on with another portion in verse 10, "None of the wicked shall understand; but the wise shall understand.”
A more correct rendering of verse 4 might be, "Many shall diligently investigate, and the knowledge (thereof) shall be increased." Here we see "the wise", i.e. the faithful Jewish remnant, searching the prophetic Word, and using it for their guidance in the day of the setting up of the abomination of desolation in the holy place (compare Matt. 24:15, 1615When ye therefore shall see the abomination of desolation, spoken of by Daniel the prophet, stand in the holy place, (whoso readeth, let him understand:) 16Then let them which be in Judea flee into the mountains: (Matthew 24:15‑16)). This has reference to the days of tribulation through which Israel will pass in the time of the end, before the setting up of the Millennial Kingdom on earth.
Ans. Not merely with melody of voice which man can hear and appreciate, but with the grace of Christ in the heart which God alone can see and love. No singing is beautiful to God that lacks this; while the feeblest song, though with a broken voice, that is the fruit of His love and grace in the heart, is sweet to His ear.
Ans. It is the day of His public appearance when He descends to the Mount of Olives to reign over the earth.
Ans. We understand this to mean that God is the gracious Preserver of all, but especially of those who believe. God takes care of sparrows. (See Matt. 10:2929Are not two sparrows sold for a farthing? and one of them shall not fall on the ground without your Father. (Matthew 10:29).) You ask, "In what sense is Jesus the Savior of all men?" and then quote 1 Tim. 4-:1. Now we adoringly own Jesus as God over all, blessed forever; but the apostle in verse 10 is not speaking of Jesus in His saving work, but of God in His gracious Providence. Scripture is divinely accurate. You never find any distinction without a difference. We must ever remember this.