Rom 3 vs 3-4(a): True, some of them were unfaithful; but just because they broke their promises, does that mean God will break His promises? Of course not! Though everyone else in the world is a liar, God is true!
Is that not awesome? People may break their promises to us, we may fail others too, but God's word...IS HIS WORD... and ... HE WILL NOT BREAK IT!
This tells me that I can trust EVERY word in the bible. Not just those that sound doable, but also those that seem impossible, far out of reach. It may sound impossible, but for God ALL things are possible and HE WILL do as He has promised. His word says so.
Prov 30 v 5: Every word of God is pure; He is a shield to those who put their trust in Him.
My encouragement to you is to KNOW the WHOLE of God's word IS true and FOR you.