His words, Exalted is He:

And they were only commanded to worship God, devoting religion purely to Him

He said:

All knowledge is concerned with acts (ḥarakāt),^{1Tustarī may be indicating here knowledge of outward conduct according to fiqh, such as the manner of ablution, the movements of prayer, etc.} until the person attains sincerity (ikhlāṣ). Then when he reaches sincerity, he will attain profound peace (ṭumaʾnīna).^{2That is, peaceful assurance in heart and mind. On ṭumaʾnīna see Tustarī’s commentary on 2:260 and p. 30, n. 92.} For the one whose knowledge [has become] certainty (yaqīn) and whose works are [done in] sincerity, will find that God removes from him three things: anxiety (jazaʿ), ignorance (jahl) and action (ʿamal), and will grant him patience (ṣabr) in exchange for anxiety, knowledge in exchange for ignorance, and the abandonment of choice in exchange for action — but this will only be the case for those who have full awareness of God (muttaqūn).^{3That is, reading ʿamal instead of ʿilm according to MSS F638, f. 68a and F3488, f. 320b.}

He was asked, ‘And what is sincerity (ikhlāṣ)?’ He replied:

It is responding (ijāba), and whoever does not respond has no sincerity.^{4See the commentary on 39:11 above, and IT, pp. lvi–lvii.}

He also said:

Sincerity has three facets: worshipping purely for God (ikhlāṣ al-ʿibāda li’Llāh), acting purely (ikhlāṣ al-ʿamal lahu) for Him, and [keeping one’s] heart purely for Him (ikhlāṣ al-qalb lahu).^{5This translation has attempted to take into account the other meaning of ikhlāṣ, namely being ‘purely for’, ‘freed for’ something.}

His words, Exalted is He:

…This is [the reward] for him who fears his Lord.^{1The rewards that are mentioned in the first part of this verse are: Gardens of Eden beneath which rivers flow, wherein they shall abide for ever. God is pleased with them and they are pleased with Him…}

He said:

Fear (khashiya) is [experienced] privately, within [lit. is secret, sirr], whereas humble submission (khushūʿ) is shown openly (ʿalāniyya). As for the one whose bodily members are in a state of humble submission, Satan will not approach him.

He was asked, ‘What is humble submission (khushūʿ)?’ He replied:

It is standing before God and being steadfast (ṣabr) in that.^{2That is, maintaining a state of awareness of the presence of God at all times. Ṣabr in this context has the meaning of endurance and perseverance, rather than patience as we would usually understand that word in English.}

He [continued]:

The perfection of fear [of God] (khashiya) is the abandonment of sins, [those that are committed] both in secret and openly.