Charles Spurgeon Commentary Hebrews 6:16-18

"For men swear by the greater: and in every dispute of theirs the oath is final for confirmation. Wherein God, being minded to show more abundantly unto the heirs of the promise the immutability of his counsel, interposed with an oath; that by two immutable things, in which it is impossible for God to lie, we may have a strong encouragement, who have fled for refuge to lay hold of the hope set before us:" — Hebrews 6:16-18 (ASV)

It seems a great change in this chapter from the sad tone at the beginning to the joyous note at the end; but, indeed, there is no contradiction between the two. Paul is simply giving us two sides of the truth, – both equally true, – the one necessary for our warning, the other admirable for our consolation. God will not leave you, my brothers and sisters; he has pledged himself by covenant to you, and he has given an oath that his covenant shall stand. Therefore, take courage, and press forward in the divine life, for your work of faith and labour of love are not in vain in the Lord; so let us lay hold upon the hope set before us: