Simple is easy to understand, humble or lowly, free of deceit or guile and sincere, not complicated, not elaborate or artificial.
Preaching the truth means an agreement with a standard of original scriptures. It is the unconditional truth of God, honesty; integrity; truthfulness.
God is the one Supreme Being. God is the creator and ruler of the universe, the alpha and the omega, the first and the last, the beginning and the end.
But God, who is rich in mercy, because of His great love with which He loved us, even when we were dead in trespasses, made us alive together with Christ (by grace you have been saved)