The tashahhud is praise of Allah. Be a slave to Him in your innermost being, fearful and humble to Him in action as you are His bondsman by word and claim. Join the truthfulness of your tongue to the pure truthfulness of your innermost being.
He created you a slave and commanded you to worship Him with your heart, your tongue and your limbs. Realise your enslavement to Him by His lordship over you. Know that the forelocks of creation are all in His hand. Creatures possess neither breath nor sight except by His power and will: they are incapable of bringing forth the least thing in His kingdom, unless it is by His permission and will. Allah said,
Your Lord creates and chooses whom he pleases; to choose is not theirs. Glory be to Allah, and exalted be He above what they associate [with Him]. (28:68)
Therefore be a slave to Allah, remembering Him by speech and proclamations, and join the truthfulness of your tongue to the purity of your innermost being, for He created you. He is too mighty and majestic for anyone to have will or volition except by His earlier will and volition. Fulfill the state of enslavement by being content with His wisdom, and by worshipping in order to carry out His commands.
He commanded you to send blessings upon His beloved Muhammad, may Allah bless him and his family and grant them peace. Therefore join your prayer to Muhammad with your prayer to Allah, obedience to Muhammad to obedience to Allah, and your witnessing of Muhammad to your witnessing of Allah. Watch out that you do not miss the blessings of knowledge which are contained in one’s respect for his sanctity, with the result that you are denied the benefits of the prayer on him. Allah commanded him to ask for forgiveness for you, and to intercede for you when you perform what is obligatory in the command and prohibition, and in the sunnah and courtesies (adab) demonstrated to man through the Holy Prophet. You should know the majesty of his rank with Allah.