"For the word of the Lord is right; and all his works are done in truth." Psalm 33:4
"All his works are done in truth". "Thy word is truth". What God does He does within the confines of His word. Even God uses His word as a boundary in which He does anything. He doesn't deviate from it, He doesn't change it, He doesn't ignore it, He doesn't work around the outside edges of it, He doesn't alter it, but He holds true to even the smallest jot and title. God didn't just give us a command not to add to or take away from His word, but He Himself will not. He doesn't change His word in "mid stream". He doesn't change it when it "looks like" it isn't working. He doesn't change it to fit the situation. His word remains the same. It is eternal and forever established and settled. "Heaven and earth will pass away but His word will remain forever."
The word truth in this verse is also translated faithfulness, fidelity, steadfast. God's word is faithful, it is steadfast, it is the truth. We can place our trust and confidence in what God says. We can place our trust in what He does because everything He does is based on the truth of His word. This is also how we are able to "try the spirits" to know if "the work" is God or not. If it doesn't line up with His word, if it's in opposition to His word, if it has no regard for His word, if it doesn't rightly divide the word, then it isn't Him. God is faithful to His own word. He is faithful to stick to it and He even swears by it. He will not do anything that conflicts with His word. Therefore, we can know what is and isn't a work of God, and we can trust what He does-- because what He does is founded upon His eternal word that is steadfast and true.
Have a great day. God is faithful to His own word and whatever He does, He does within the confines of His word.