For thus saith the Lord; Like as I have brought all this great evil upon this people, so will I bring upon them all the good that I have promised them…Jeremiah 32:42
Another clear, simple, straightforward statement regarding the certainty of God's word. My Bible labels this section of the book of Jeremiah "God's promise of a gracious return from captivity." What this passage points out is that just as surely as God kept His word in bringing judgment upon the people of Judah for their disobedience (in this case, captivity in Babylon), God will keep the promise He made to Abraham all the way back in Genesis 12, and Abraham's seed WILL one day inherit and forever possess the land of Canaan.
Back just one chapter, in Jeremiah 31:35-36, the Bible says, Thus saith the LORD, which giveth the sun for a light by day, and the ordinances of the moon and of the stars for a light by night, which divideth the sea when the waves thereof roar; the LORD of hosts is his name: If those ordinances depart from before me, saith the LORD, then the seed of Israel also shall cease from being a nation before me forever.
Though Israel was under the judgment of their God in Jeremiah's day, He told them that the nation could count on returning to their land and dwelling in it forever just as much as they could count on the sun rising in the morning and the moon coming out at night.
Likewise, the promise of eternal life for all who would call upon the name of the Lord (Romans 10:13; Titus 1:2; 1 John 2:25-26) is just as certain as the promise that those who fail to repent will indeed perish and the wicked will be turned into hell (Luke 13:5; Psalm 9:17).
I am 100% confident today that God meant it when He said the way of transgressors is hard (Proverbs 13:15), and I am fully persuaded that He was telling the truth when He said that blessings are upon the head of the just (Proverbs 10:6).
God has promised good things to those who obey His word. And He WILL bring those things to pass. Believe what He said, and walk accordingly.