always - Greek, “in every season”; implying opportunity and exigency (Col 4:2). Paul uses the very words of Jesus in Luk 21:36 (a Gospel which he quotes elsewhere, in undesigned consonance with the fact of Luke being his associate in travel, 1Co 11:23, etc.; 1Ti 5:18). Compare Luk 18:1; Rom 12:12; 1Th 5:17.
with all - that is, every kind of.
prayer - a sacred term for prayer in general.
supplication - a common term for a special kind of prayer [Harless], an imploring request. “Prayer” for obtaining blessings, “supplication” for averting evils which we fear [Grotius].
in the Spirit - to be joined with “praying.” It is he in us, as the Spirit of adoption, who prays, and enables us to pray (Rom 8:15, Rom 8:26; Gal 4:6; Jud 1:20).
watching - not sleeping (Eph 5:14; Psa 88:13; Mat 26:41). So in the temple a perpetual watch was maintained (compare Anna, Luk 2:37).
thereunto - “watching unto” (with a view to) prayer and supplication.
with - Greek, “in.” Persevering constancy (“perseverance”) and (that is, exhibited in) supplication are to be the element in which our watchfulness is to be exercised.
for all saints - as none is so perfect as not to need the intercessions of his fellow Christians.