“Neither by the heaven, for it is the throne of God,
Nor by the earth, for it is the footstool of his feet,
Nor towards Jerusalem, for it is the city of the great King.
Nor shall you swear by your head, for you cannot make one hair white or black.”
The type of oaths that He is speaking of is now made clear. They are those which are not directly made in the Name of the Lord (as court oaths mainly would be, for solemn emphasis) but those which used circumlocutions. Oaths made ‘by Heaven and earth' were later seen as not being made ‘in the Lord's Name'. Those ‘towards' Jerusalem were, but that was determined later. But such would not anyway be a solemn oath in court in terms of the requirements of the Old Testament (and thus ‘the Law'). It will be noted that He makes no reference to oaths actually made in the Name of the Lord. This helps to confirm that Jesus is not referring to solemn court oaths.
Jesus then gives His reasons why they should not use such oaths. All of them are the equivalent of being ‘in the Lord's Name'; an oath ‘by Heaven', because Heaven is the throne of God, an oath ‘by earth' because it is His footstool, an oath ‘towards Jerusalem' because that is the city of the Great King, and an oath ‘by my head' because it is God who created it and is its Overlord as is demonstrated by the fact that they cannot alter their age, making themselves white-haired and therefore older, or black-haired and therefore younger. They may dye their hair all they like, and hair dyes of a kind were known at the time, (hair dying was certainly practised in Egypt), but they could not alter what they essentially were. God was in total control of that.
Here Isaiah 66:1 ‘Heaven is My throne, and the earth is My footstool' and Psalms 48:2 ‘Mount Zion in the far north, the city of the great King', are in mind. Note the emphasis in each case on God's Kingly Rule. Both Heaven and earth are in the throne room, the One the symbol of His sovereign power, the other the symbol of His worldwide authority (compare Matthew 28:19). Jerusalem is His city and therefore the scene of His Kingly Rule, and He has absolute and acknowledged sovereignty over His disciples' ‘heads' and therefore over their lives. So those who are His and under His Kingly Rule will not debase what is His by calling on them in unnecessary oaths. They will rather give due honour to their King. Nor do they need to do so for they will always speak as those who are in the presence of the King.
Here then we have a picture of the whole Kingly Rule of Heaven, the throne room with its throne and footstool, the King's city and the King's ‘heads', His men and women. In the Psalm the great King is God Himself, but here there may well be the thought that it includes Jesus, even though His kingship has not yet been spoken of openly in front of the disciples. They will learn of it in the future (Matthew 16:16; Matthew 16:27-28; Matthew 17:5; Matthew 17:25-26; Matthew 19:28; Matthew 20:21; Matthew 21:5; Matthew 24:30; Matthew 25:31-46). Note how in the parables in Matthew 18:23-35; Matthew 22:2-13, the King is His Heavenly Father (e.g. Matthew 18:35) while by Matthew 25:31-46 the King is Jesus Himself. In the words of Paul, ‘we have been transferred (from the tyranny of darkness) into the Kingship of His beloved Son' (Colossians 1:13). The reader, however, knows all about the emphasis on His kingship from previous Chapter s.
The combining of their ‘heads' with the other three symbols of royalty is an indication that Jesus is speaking to those who acknowledge His rule within the Kingly Rule of Heaven. Their heads also are royal, with their hoary crown or otherwise, as given by God. Note how in the Psalm the Jerusalem spoken of is very much an exalted Jerusalem, ‘beautiful in elevation, the joy of the whole earth', all tremble before it, and it is very much God Who has exalted it. It is the symbol of Heaven on earth. Note also the contrasts here, Heaven with earth, the exalted royal Jerusalem with their heads. God rules over all.