His word will not return void.

 Isaiah 55:11

So is My word that goes out from My mouth: It will not return to Me empty, but will accomplish what I desire and achieve the purpose for which I sent it.

God's word is truth and it is life. This verse confirms that His word that comes out of His mouth, will not return to Him void, but it will do that which was meant. This means all the promises that God has made to you, whether they have materialized or not, they will manifest. If He told you that He will never leave you nor forsake you, best believe it because that is true.  He will keep to His word.

What we need to remember though, is that His timing is not the same as ours. We may want things to happen now, immediately, when actually His plans are  not aligned with ours. This doesn't mean that He has failed you or has forgotten you, no! It could be that He is preparing that which He promised you, or maybe He is preparing you for that which He promised you. Or it could be that He is building your character, to be more patient. Thus, it is very important to hold on to His word, no matter how the situation looks. What He promised, He will fulfill. The devil may come and whisper wrong things to discourage you and steal your faith, but you just need to hold on to His word. His word will accomplish its purpose.