‘And we have more sure the word of prophecy, to which you do well that you take heed, as to a lamp shining in a dark place, until the day dawn, and the day-star arise in your hearts,'
The words and experience on the holy mount had made more sure the word of prophecy, spoke in earlier days by the prophets. Thus there were many witnesses to His power and glory. And they would do well to take heed to them. For they were like a lamp shining in a dark place (see Isaiah 9:2-7; Isaiah 60:1-3; compare Matthew 4:16-17), which would go on shining ‘until the day dawn and the day-star arise in their hearts'.
There are three ways of seeing this;
1) As meaning that they are to allow prophecy to be like a lamp shining in the darkness (compare Psalms 119:105), until the Day comes and His glory is more fully manifested in their hearts, something which will happen at His second coming resulting in eternal Day (Zechariah 14:6-7).
2) As recognising that the day-star arises in the darkness and actually precedes the dawning of the day, and thus seeing it as meaning that through prophecy the day star will arise in the hearts of true believers leading on to the dawning of the Day.
3) As seeing it as a present experience which they can have, just as the disciples had had it on the mount, with the light of the glory of God which is in the face of Jesus Christ shining on them (2 Corinthians 4:6) making manifest His glory and making them children of the day (1 Thessalonians 5:5). Compare John 12:35-36; John 12:46.
Whichever way we take it the point is that the light of the full glory of Christ is to dawn on them, and they are to see Him as He is. All are in fact true. For through His word the glory of Christ does shine in our hearts, and one day in accordance with its promises we will behold His greater glory, either when we go to meet Him, or when He comes in His glory.
In regard to this Isaiah had spoken of the coming of God's king in terms of a light shining out of darkness (Isaiah 9:2), which would result in the child Who would be born and the Son Who would be given, on Whose shoulder would be the Kingly Rule, Whose name would be called Wonderful, Counsellor, Mighty God, Everlasting Father, Prince of Peace (Isaiah 9:6), and for Whom of the increase of His rulership there would be no end, so that it would be established and upheld with justice and righteousness from henceforth and for ever (Isaiah 9:7). This includes both present and future aspects and the point may be that they would do well to take heed to it.
In mind also may be the prophecy of the coming of the star from Jacob (Numbers 24:17), which together with the picture of Jesus coming as the morning star which is found in Revelation 2:28; Revelation 22:16, would again include both present and future aspects.